Thanks for your post anyway.
I still think that the signal strength (even with the theoretically improved aerial) is only just borderline and hence that a cheap signal booster will fix the problem.
Chris
PS: Beware of many local so-called professional aerial fitters. Many of them don't have a clue about signal propagation and reception. I recently asked a local guy how much he'd charge me simply to go up a ladder and fix my drooping aerial back into the correct position. I might well have paid him the £40 he wanted if he hadn't started telling me loads of complete rubbish about the digital changeover (in the hope of getting far more money out of me). I told him that I've had articles published on the subject, and sent him on his way. He was a cowboy and I suspect that many other aerial fitters are as well.