I offer you a solution James - move house.

I'm sure someone could tell you which area has the best coverage, but
I guess you'd find house prices inflated there because of the
availability of the signal. That might put you off the idea.

Incidentally, I have a Casio watch that is still on the market for
about a tenner. But I won't part with mine as it is accurate to 1
second per month. But the straps wear out. So I pay a fiver every
two years or so for a new strap. I guess I must be on number 5 or 6
by now. I have a back-up watch but that's rubbish and drifts by the
best part of two seconds EACH WEEK!

Jack