Generating arithmetic quiz questions
Looping

You want to perform an action 10 times. The loop counter never matters for your code, you just need to ask 10 questions. The way you wrote the code, you have:

count = count + 1


in 6 places, all of which are necessary, otherwise you would loop too many times. That is very error prone. If you added support for division, you would have to write it two more times. Good rule of thumb is never repeat yourself! 

The best way to loop 10 times in Python, when you don't care about the loop count, is:

for _ in range(10):
    # stuff


No need to worry about incrementing count. Let range() do it for you.

Don't Repeat Yourself

The code for adding, subtracting, and multiplying is the same. The only difference is what operation you do and what operation you print. You mostly already have that refactored. You do use op() to perform the operation. So let's just go one step further:

ops = (('+', add), ('-', sub), ('*',mul))
op_name, op = random.choice(ops)


And then, I'm pretty much copying your logic for add with just one real change (and renaming some variables):

print("What is", x, op_name ,y, "? ")  # op_name, not +
actual = int(input())
expected = op(x,y)
if actual == expected:
    print("Well done, this is correct!")
    score += 1
else:
    print("Sorry, but this is incorrect.")


I also renamed your variables to actual and expected, instead of question and answer - since question didn't really refer to a question. Also += 1 is a more concise way of expressing incrementing by one.

Tell the user the answer?

If the user gets it wrong, do you want to tell them the correct answer?

Finishing up

You don't need to check count (or, now, _) to know when you're done. Just wait for the loop to end, at which point you can print the score. So the flow looks like:

score = 0
for _ in range(10):
    # prompt a problem and potentially increment score

print("Well done "+name+"! You have completed the quiz. Your final score out of 10 is "+str(score)+".")


Though typically you'd express the score as X/10, not out of 10 is X. That just reads funny.