He appears to be in breach of the lease - but that is a civil breach involving the agreement between him and the freeholder. Get onto the freeholder - but you may not get any joy.
When was the property converted? - there are now minimum standards under Building Regs that define the annuation of noise that must occur between floors - just to stop this very situation. Can't remember when these came in - about 6 years ago, I think. Can be checked out, but pointless if the conversion is older than that since the requirements are never retrospective. If there is any mileage on this issue, it will be for Building Control (one of the departments at your local council) to take up with the owner of the building (freeholder).
The only other angle that I know of is the anti-social behaviour one, based on excessive noise. This again is a civil action but only the local authority can pursue such actions with the individual concerned. You are going to have to keep a diary with times etc. - initially try speaking with the Environmental people. If they are willing to pursue anything, Ibelieve they have a right to ask for money from you to investigate - often a few hundreds of pounds.