hi
Most stockbrokers will offer different currency accounts and if you are buying in sterling / USD and want to settle in those currencies, you will have to pay for them in this currency.
The main issue is when selling. Depending on the companies you're investing in, the FX rate between EUR/GBP/USD wouldn't really be affecting the individual share price. If you have different currency accounts, when selling, you can keep the proceeds in GBP/USD or request EUR - depending on what your currency view at that time is.