You had me in for a while: But I think you will all find that 100 GBX= 1 GBP
Any differential is caused by people using Commercial Money Changers currency rates to do their conversions, they always discount the official exchange rate to give themselves a profit margin.
If in doubt look up the balance of your trading account and divide by the number of shares, I am pretty sure you will find that your stockbroker uses the Official Exchange rate which is currently $1=0.555 GBP or 55.5p