Pedal stuck to arm

[Richard A Thackeray]

I also tried using a spanner to hold the pedal whilst trying to turn the alan key.

Erm..... could this be the reason???
You're using your strength against yourself??
Your description reads (to me, anyway), as though you're trying to hold the crank in a fixed position, whilst attempting to remove the pedal with the allen key

 

[Profpointy]

Do make sure it's being turned the correct way. I'm sure you know one pedal has a left hand thread, but it's fairly easy to mix up how you visualise the LHThread pedal and end up bollocking it up even tighter - even though you've convinced yourself....

....not having a dig, after all, how do you think I know this?

 

[livpoksoc]

In the end I gave up & went to my lbs who charged a reasonable £5 & agreed that it was a tight thread with no grease and they had to use a long armed tool to loosen it off.
Thanks for everyone who contributed though, appreciated!