I've got Dunlops on my Octavia vRS and just had a puncture. It turns out that there's a small split in the sidewall on the offside rear which takes about 2 days to go completely flat.  I've been to my local tyre place and it's a "sorry mate, no can do" in terms of fix and a new tyre is needed at just short of £100. Sound right or is he pulling my chain ?

I have been told by tire fitters that they are not allowed and also that it is impossible to repair the sidewalls due to the flexing 

I don't know about the cost of a new tire though

You will also find that they won't repair punctures that are within the main tread but 'close' to the sidewall as well.

Bite the bullet mate, spend the 100 (+) squids, it may save your life!

No they're correct. Not sure how you'd expect a split to be safely repaired?