It depends on the euro / pound exchange rate at the time you get your cash.
The leva is 'pegged' against the euro, so that will always remain static (the rate you can get now, should be the same in a few weeks). However, the pound isn't pegged against the euro, so the exchange rate will fluctuate if one currency gets stronger or weaker.
My advice would be to leave it as long as you can before your trip and then see which is giving the best rate at the time.