On Sun, 20 Feb 2011 21:35:42 +0000, Roger Mills wrote:

Ask in uk.tech.digital-tv One of the main posters there is Bill Wright,
who does it for a living (but not in your m-i-l's area).

He also helped set up this site:

www.paras.org

Have a read before you shell out. Chances are if the set top aerial
delivers a picture now, it'll handle the digital just fine.