There was a unit based in Bristol (Was called Dti now I think called Oftel) who are responsible for radio interference. They will monitor after a complaint and if the mower is producing over the permitted level of RF then he would be forced to correct it.
However more neighbourly approach would be to ask him to fit suppressor plug cap and ensure all cowling's are in place.
Aiming aerial, Using narrow band, Good quality coax, will all help.
Look here
http://www.ofcom.org.uk/complain/inter/[/QUOTE]
werd! I had a CB radio back in the '80's, and my neighbours complained about TV interference (4W power!), legally obliged to buy them a suppressor for their TV, job done.
As stated above, rather than replace the aerial, much of the time the lead is the problem, with splits, that induce water ingress. Seen many tuners full of water due to this. No need to replace the aerial.