BINGO!!!!!
Chris's suggestion was bang on. The amplifier is designed to plug into the mains close to one of the TV sets. A short fly lead connects this to the TV and the coaxial cable connects it to the first F socket on the aerial body. This then amplifies all the outlets. I found I had an excellent signal on the first TV so to save time, I connected a second length of PF100 to the aerial body and ran it to the 4 way junction box which connects to the roof aerial and serves the remaining TVs. All that remained was to swap this lead with the roof aerial lead and I'd connected all 3 other sets to the new aerial. Fingers crossed that the amplified signal would be strong enough to be spilt 3 ways, I checked and retuned each TV and found all are working very well indeed.
Hoorah!!!! Can't say how happy I am!!
Sincere thanks to all contributors to this thread, without whom I'd probably have no hair/fingernails left, not to mention Mrs Osem's boot wedged firmly up my backside!!
I think the original cable was a big part of the problem with the reflections so investing in decent PF100 was well worth it. The other thing is that the aerial is only temporarily located in the loft at the moment and needs fixing to the woodwork and orientating towards the transmitter more accurately. No doubt this will improve matters further.