I sympathize, I know that  buying Bitcoin is pretty hard for newbies, especially since you picked a bad time (there's a lot of pressure on the Bitcoin network right now so all transactions are pretty difficult).  Companies which let you buy with a debit/credit card are OK if you provide ID and choose a trusted one.  I think that most sites, like Coinify and Coinmama are okay with GBP but I can't 100% vouch for that.

Alternatively, if you're in an urban area you could try a Bitcoin ATM which make it a bit easier for you to transfer the funds to your wallet (you do need a wallet to hold your Bitcoin, like Coinbase or Blockchain).

You could even do a transfer on LocalBitcoins which is more of an open marketplace where you can do transactions with cash (DON'T do PayPal, there's a likely chance of chargeback fraud).