UK stock trading platform

Hello

I am currently using Plus500 on a demo account. Doing well although this says little about future success on a live account.
Although I like the variety which Plus500 offers such as Commodities as well as Shares and Fx the range of shares seems slightly limited.
I have been looking around for other platforms and many have a flat free per trade of £8 for example or a monthly contract/membership. Is this common among all good platforms?
I had my eye on CMC however have seen some threads about how they are not good and that IG Markets are a better alternative.
What would be a good platform for Share trading and the possibility of scalping.
:help:

Just a quick example about what I mean by limited shares, Plus500 does not offer Santander (STD). I wanted to short this stock Tuesday 1st Midday at ~6.40 a share. Just found out that I would have made a ~5.80% profit.

Very interested in the answer too. Subscribed!