This is a 1972 remake of the 1946 original,with most of the original cast.Update today 12 July the 20 episode Dick Barton - Special Agent: The Cabatolin Diamonds has started on Radio4 extra
http://www.bbc.co.uk/programmes/b036v8py#play

Definitely one of my all-time favorites.
For that person who inquired here and any others that want more, there are quite a few Dick Barton series...usually 26 episodes each.
They are out there in quite a few sites but I belong to, and have so for 10 years, a site which will be able to help you with the other stories in the series.
The site is..
otrplus.com
Tell 'em pizzaman sent you and see you there.

Absolutely top notch. Great to hear these series again.

My question is:

For a serial that ran for that long - from 1946 to 1951 - there are only 10 episodes that still exist?

Seems a bit odd.

Absolutely brilliant - makes me 12 again !!!

Dick Barton was a phenomenally popular radio hero in post-war Britain. Probably only Paul Temple and The Goons rivalled his fame. In 1972, as part of the BBC's Golden Jubilee celebrations, the two stars of the show came together once more to re-record the very first adventure, which is what we have here.

Barton is obviously inspired by the Bulldog Drummond style heroes of the 1930s, a strong silent type who is at a loose end after the war but revels in grappling with mad scientists, secret weapons and mysterious assassins.

It's not subtle, but it's a lot of fun and the cast captures just the right thrill-a-minute atmosphere of the old serials.