What is the following pattern called?
Yes, that is a quilted pattern. Quilting refers to the process sewing three layers of fabric together, usually two layers of woven cloth on the outside, with a layer of insulation sandwiched in between.
You can absolutely buy quilted fabric. Any sewing supplier with a large selection of fabric should have some, but usually not a huge selection. You might find some in the &quot;home décor&quot; section of the store as well as in garment fabrics. You can also sometimes get &quot;quilted insulation&quot; or &quot;quilted batting,&quot; which is quilt batting / insulation with fabric only on one side of it. You can use it as the lining for another garment, but the quilting pattern would only be visible one side.
Bedspreads are often made of quilted fabric; in fact the specific stitch pattern in your example is exactly the same as a quilted bedcover I had years ago. So if you don't find what you're looking for as &quot;by the yard&quot; fabric, have a look at premade bedspreads. In fact, it can sometimes be less expensive to buy a finished item than fabric by the yard. (Why? Ask an economist.)
As to the actual fabric material, that looks to me like a synthetic fiber. The fabric might be rayon or nylon. Ideally you would want to go to a fabric store, feel the fabrics and talk to a salesperson about which fabrics would work best for a coat. Second-best would be talking to someone on the phone, at a store dedicated to selling fabric for sewing, so they really know how to advice you on what fabric would be best for a given purpose. If you have to buy online, look for fabrics that are specifically intended for outer garments. The main concern is that you buy something that looks great in a photo, but that isn't actually sturdy enough to hold up as an outer garment. However you buy your fabric, you'll get the best advice about specific products from a store that's dedicated to selling fabric and sewing supplies, rather than a more general &quot;arts and crafts&quot; store. This list in The Guardian of &quot;Top ten fabric shops in the UK&quot; might be a good place to start.
If you quilt your own fabric, it's important that the fabric layers are densely woven enough to hold in the insulation. If you make a quilt with loosely woven fabric, the insulation will work its way out over time, creating unsightly &quot;pills&quot; on the outside. Outdoor DIY gear suppliers usually sell both fabrics and insulating layers, and they usually provide guidelines on which combinations will work together. A few of my favorite suppliers of materials for making my own outdoor gear are: ripstopbytheroll.com, therainshed.com and diygearsupply.com. Sorry, I have no idea if any of them ship from within the UK. Note that if you start with a waterproof outer layer of fabric, then quilt it, it stops being waterproof because you just punched a bunch of holes in it.
Making your own quilted fabric will take at least as long as sewing a jacket out of it. If that doesn't sound like fun to you, I definitely recommend just buying premade quilted fabric. If you want to make your own quilted fabric, keep reading.

How to make quilted fabric
This is just a short summary. As with most hobbies the additional information that exists could fill a small library. I include a few links to more references at the end. Quilting as a hobby has been popular for centuries, so your local library surely has a few books.
Materials:

two layers of woven fabric - these can be the same fabric or different
a layer of quilt batting
large safety pins
thread
a sewing machine, or a quilting hoop and a hand sewing needle
a fabric marking pencil (or other fabric marking method; more details below)


Get your two layers of woven fabric. As with most sewing projects, before you begin the fabric should be washed, selvedges trimmed off, and ironed. Get a piece of batting the same size (don't pre-wash it).

Lay the bottom layer of fabric out flat, with the &quot;good&quot; side facing down. The &quot;good&quot; side is whichever side of the fabric you want visible; the other side will be hidden.

Lay the batting on top, smoothing out any wrinkles.

Lay the top layer of fabric on top, with the good side facing up. Again, smooth out any wrinkles.

Tack the three layers together at regular intervals. The point is to secure the layers so they will stay in place when you move the quilt to sew it together. Large safety pins work well for this - they actually make special quilting safety pins that are bent, which lets you more easily put then into the fabric. Regular pins aren't a great idea - some will fall out, and you'll stab yourself a lot as you manipulate the quilt.

(Optional) Mark your stitch pattern on the top of the quilt. Make sure whatever you use to mark the pattern is 100% removable. Quilting suppliers sell a wide variety of supplies for this, and there are lots of DIY methods.

To draw the design freehand, a scrap of white bar soap or a piece of white chalk works okay for a few marks, but if you're doing a lot of marking a fabric marking pencil is worth the few dollars it will cost.
You can draw the design freehand or use a stencil. You can buy premade stencils or make your own. Premade stencils come in a huge variety of designs, from simple to very intricate. For a simple design like in your example, I would make my own by cutting a wavy edge on a long piece of cardboard.
A stencil with lines cut out of it (as opposed to a simple edge-trace stencil) allows you to mark the fabric by just wiping chalk powder over the stencil. Brand names include &quot;Miracle Chalk&quot; and &quot;Pounce Pad.&quot;

If you buy a fabric marking tool like the pencils or dust pads I mentioned, read the reviews and be sure to get one that's easy to remove. White chalk fabric pencils or marking dust tends to come out fairly well, but blue or other colors of chalk have a reputation staining the fabric.

Fold or roll up the pre-quilt from both edges, leaving the middle unfolded and exposed. Working from the middle of the quilt out to the edge, use a straight stitch to sewing along the marked lines (if you marked them) or freehand sew it. There are a lot of tips and tricks that will help you do this smoothly and efficiently, so instead of trying to list them all here, I made a list of references.
Quilting on a home sewing machine:

https://www.generations-quilt-patterns.com/how-to-machine-quilt.html
https://suzyquilts.com/how-to-machine-quilt/
https://www.diaryofaquilter.com/2019/03/how-to-plan-your-quilting-from-christa-watson.html

Quilting by hand:

https://suzyquilts.com/how-to-hand-quilt/
https://www.thimblelady.com/hand-quilting/

In case you want more references or these links go dead, useful search terms include &quot;machine quilting&quot; or &quot;sew a quilt on a home sewing machine&quot; (if you're using a sewing machine) or &quot;hand quilting&quot; (if you're sewing by hand).


Note also, that many people who make piecework quilts will either send out their assembled quilt to be professionally quilted, or they will rent time on a long arm sewing machine at their local quilting supply store. Quilting by hand or on a home sewing machine is just not everyone's cup of tea.

Offset Wavy Line Top Stitch Pattern
The actual top stitch pattern in your example is just made of wavy lines, with each wavy line offset from the one next to it, so the bottom of one &quot;wave&quot; almost lines up with the top of the &quot;wave&quot; in the adjacent line. It's such a basic design I couldn't find a name for it, even though I'm sure it has one. I made these outlines in Microsoft Paint.
To draw it, make a stencil with a wavy edge, like this:

Stencil one wavy line, then add a second wavy line offset, like this:

Continue adding wavy lines until you hit the edge of the fabric. Notice how the &quot;onion bulb&quot; shape appears as you add more repeats.

With a bit of practice, you could probably sew this design freehand. You might want to mark out a grid on your fabric to keep your midlines parallel and your peaks and valleys lined up, but you could do that by placing your safety pins in a grid pattern.
Tip: Curves are difficult to sew. Straight lines are much easier. If you're not wedded to this specific stitch pattern, consider using a simple diamond grid pattern. You don't even need a stencil for this one, just a ruler and long straightedge. Use the ruler to draw evenly spaced  marks along one edge. Draw marks along the adjacent edge, using the same spacing. Use the straightedge to draw lines connecting connect those marks. Repeat for the other two sides. Using the same spacing on both sets of sides will give you 45 degree oriented square diamonds. Using different spacing on each set will give you different angled diamonds.
45 degree diamond grid:

(image source)
60 degree diamond grid:

(image source)