Don't use the ones from Maplins, they won't be right, you can get the CTS ones from BK or Allparts UK, as rinse_master says, around £4 to £5, or you can get the genuine Gibson ones from Rosetti, they're £9.50 so you're paying a bit for the 'Gibson' stamp on the bottom! If it's a Gibson LP, you'll need the long shaft ones, Epi LP uses standard shaft.
Having said that, a few crackles is usually down to dirt, so it would be worth trying some switch cleaner on the pots first. Have a look also at your jack socket (four screws removes the jackplate so you can have a look), if this is at all worn it's worth replacing with a Switchcraft one at around £2, again from Allparts. LP switches give very little trouble and can always be stripped, cleaned and the contacts cleaned with fine abrasive paper. That's it really, very simple electrics.