....you need an antenna which covers more of the UHF TV spectrum than the one which receives old-fashioned analogue BBC/ITV ....
We..ell, yes and no.
I took a chance with a digibox and hooked it up to my attic amplifier/distribution system and the result was good.
In fact, before the change Channel 5 was its usual snowy self off normal air. But through the digibox fed by the normal hi-gain antenna inside the attic the result is as good as all the other 20 or so channels.
Beags may be right in principle but it could just be worth a try before you fork out for a new antenna.