Phone the environmental health department of your council and ask them to send a noise abatement officer round.They will assess the level of noise and if they think it necessary they will impose an abatement order on the neighbour.
Well what time do they go go to bed? because if it was me I would go round there 10 minutes after the lights go out and wake them up and I would keep doing till they stopped annoying me.
cant believe no1s suggested jus goin round and havin a word... sure theyd appreciate it more from you first instead of jus goin to higher authorities... they may not even know u think it an issue.