Andrew, you say you are near Luton. Coverage area will be less than shown on the application I've linked to, Ofcom make the decision about power used and any need for the antenna to be directional or have nulls in it's radiation pattern as new DAB multiplexes have to avoid reducing the coverage area of current ones and, given this, and which is the best frequency block for them.

They've given them block 7D. Coverage area of the application 71% of the population in the advertised area, coverage area now 66% of it. Coverage very good in Luton, not in Dunstable, comment on the Luton Town football forum says there's a hill shielding it, reception fine in Houghton Regis.

Outdoor coverage will be better.

I can get the Cambridge SSDAB here 8 miles outside the mobile coverage area. Have a sensitive DAB radio with stereo speakers, 2nd top floor flat, ground is flat between here and Cambridge. Can receive it on the window ledge of my bedroom, kitchen and bathroom all facing towards the transmitter, have to the receiver in one small area of the window ledges though. 48kbps DAB+ Caroline and Flashback use is excellent quality.