Right, Mike, after living away from St Brides Im struggling to think where you are Ive looked on Multimap etc but Railway View isnt on there (and it's too early in the morning to bother mum). I think you must be up the road past the Scout Hall, possible near to Sally Thomas's house. If this is the case, like my sister, youll probably be getting Wenvoe (as you should) and Mendip off the back of your aerial. When you set up your set top box it would have scanned for all available channels and so youll be recieving services from both transmitters. In my sisters case the solution was to manually tune the box only to Wenvoe channels.
The channels you need are as follows -
Mux 1 Channel 30
Mux 2 Channel 34
Mux A Channel 40
Mux B Channel 50
Mux C Channel 43
Mux D Channel 46
Give retuning your box a try and see how you get on. If not joy (and assuming you are where I think you are) it may be worth checking your aerial out, perhaps it's the wrong group.
Men & Motors by the way is no longer on the Freeview platform, it was replaced by ITV4. You can still get M&M but only on Satellite and cable. In your case your only option for this is satellite.
Lastly I recognise your surname, were we in school together at St Brides ?