I know its a risk leaving money on the exchange but I figure risk of loss up to £50 with a reputable exchange like Binance is acceptable to save on transfer fees.
Imho even 200-300 GBP is OK to be kept there, the risk is not that big.
Exchanges are unsafe, yes, but not *that* unsafe.
People are emphasising that money has to be withdrawn from the exchanges because some keep amounts like tents of thousands, or entire bitcoins there (and not even trading).
You should really keep an eye on the withdrawal minimum amounts and fees for the exchange you want to use.
Since you mentioned Binance, from what I see
on their fee list, minimum amount to withdraw is now 0.001 BTC (30 GBP) and the fee is half of it = 0.0005 BTC (15 GBP).
So no matter what we say, you'll basically have to keep the money in there longer, else you'll spend
far too much on fees.