Thanks for the thoughts guys. As I said sorting out any interference issues over web was always a long shot. I did have a quick google at software oscilliscope programs but it started to remind me too much of O level physics and soon went over my simple head
I think my plan will be to run the next 2 meetings with 40Mhz - 2WD at TORCH this week and then 4WD indoors at DMS. If I survive with no interference then at least I can definitely point the problem at the Spektrum stuff and look at replacing with KO 2.4.
Still find it odd that 2 different modules and three receivers should all start having problems at the same time. The 3 receivers have all definitely had a reasonably amount of use in 5/6 years in various 12th, touring cars and buggies so maybe just time to renew.
Cheers
Rob