I have Freeview using a cheapo Wharfedale tuner + hard disk recorder.

The tuner says that the signal strength is 100% (drops to 80% occasionally).

On most of the channels I watch (BBC1 ... Channel Five, BBC4, UKTV
History/Dave) performance is perfect. One small thing though --- some
faint video background appears on Channel Five --- perhaps visible on C5
because I was watching cricket with its ample plain background; but no
breakup on C5.

However, specifically on Channel 4 + 1 and More 4, I get breakup; while
that is happening, the signal strength indication remains good (I say
that because there is a tree between my aerial and the transmitter and
there has been a lot or rain recently.

I have RF entering the Freeview tuner/recorder and then off to the VHS
recorder. Otherwise SCART connections --- assorted breeds acquired randomly.

Any suggestions as to the cause?

TIA,

Jon C.