The current issue of Which magazine has an article about the 'digital rip
off' and how many people won't need a new aerial to get decent digital
reception, despite the warnings of some aerial fitters.

They also mentioned a self-test that you can do to gauge your own reception.
If you go to Teletext/Ceefax page 284 on BBC1, BBC2, ITV and C4 in turn you
can view a test grid that shows the quality of the signal. Any missing
blocks on any of the channels means you may benefit from a new aerial, but
if all the grids are complete, you should be OK.

I thought I'd update the Digital TV page on DIYfaq wiki, but it seems to be
locked for edits.