it fluctuates, because the markets do. the only time 1pip will equal £1 forever is if you trade XXX/GBP, anything else will change.
if you trade EUR/USD your pounds in account must first be converted to dollars and then traded against the euros.
http://uk.finance.yahoo.com/currency...submit=Convert
USD/GBP currently is 0.4881. thus trading 10k EUR/USD will be 1pip = 0.49p OR 100k will be 1pip = £4.88