So can anyone advice on a a cheap exchange site that will trade me my GBP in to BC for say a 2Ks worth? After all when there are online share dealing accounts like Trading212 giving free trades away on the London Stock Exchange and no subscription costs to have an account with them, then surly there must be something siular for BC (given the fact its only electrical computer running costs)
If by BC you mean Bitcoin then you are giving the wrong abbreviations and could easily cause some confusion. Rather than saying BC you are better off saying BTC.
About the exchange site you need my advice is that you should be ready to do your own research, there are a good number of exchange you can check out but don't use any of you haven't done your research.
Here is a list you can check.
https://koinly.io/blog/best-crypto-exchange-uk/