Halo.. Travel expert out there! I need ur help!!

Can someone please tell me where can have the best rate for changing currency, British Pound(GBP)??
As I am planning to go UK & Europe in may.. Should I change my MYR TO GBP here or there (UK)?
Same to Euro (EUR). Should I change here 1st or go to UK there change?? Which 1 is better??
And where can get the best rate for changing MYR TO GBP & EUR in KL??
Please advice me! Thanks alot!!