How will axial precession affect the weather in the northern hemisphere (UK latitudes)? Unless there's a twin star to our sun in which case axial precession might be an illusion the Earth's wobble won't effect the total amount of energy received from the sun as is expected from increased ellipticity, but will effect the amount of sun's energy to the Northern and Southern hemispheres in a cyclical 26000 (and diminishing) year period with periodic further exacerbations caused by variations in tilt.

How has Precession and variations in tilt been factored into the weather change model if at all?

As a side question: On the Salisbury Plain 6500 yrs ago according to wobble theory the East-West alignment going by the apparent motion of the sun across the sky must have been different to today. Can anyone tell me how to calculate the difference in respect to Grid North  please? 

Background:
I'm building a picture of Neolithic Britain and want to know the orientation of East-West in this time period to check for orientation practices if any. The particular time period I'm interested in lies about half way along the Axial Precession's swing so I'm interested to know A) Whether the axial precession exists or not and B) How the theory is in agreement with the weather patterns for the last 24000 yrs on Salisbury Plain.
You may be better off getting a more precise answer by cross-posting this physics if you want a precise mathematical explanation of the model. 

First, axial precession, as mentioned above, is different than axial tilt. Both change over time, but on different time scales. 

That said, the answer is it has most certainly been explored: Milankovitch cycles are an attempt to explain patterns of solar forcing on climate. The wikipedia article does a fairly good job of laying out the foundation of the theory, which is that there are three key components influencing solar forcing: eccentricity (how elliptical our orbit is), axial tilt (the change in amount of tilt of the earth), and axial precession (the actual change of direction of the poles). All three components operate on different time cycles.

Unfortunately for us, the nice Milankovitch theory leads to a huge conundrum: the predictions don't play out as expected. Physics dictates that eccentricity would have the weakest effect of the three, but the largest fluctuations are seen in roughly 100ky intervals (tilt and precession operate on roughly 25k and 50k intervals, eccentricity roughly 100k). This leads to the 100,000 year problem. 

Now, all of this is in the context of climate on the global scale, but the point applies just as well: nobody has a conclusive answer as to what exactly is going on, hence the entire field of paleoclimate. Unfortunately for scientists, the Earth is far from a simple rock: our physical (ocean, atmosphere) and biological systems are so complex that it is often too simplistic to pin down changes on one particular phenomenon on a geological time scale. People can study the temperatures  of individual sites over time, but determining the big picture cause of those fluctuations is tough enough for the planet as a whole, much less for a location as specific as the Salisbury Plain.