Old TV programme: 'Mr Smith's Airship'

This might be something only the Brits could answer, unless the BBC sold the programme in question abroad, but here goes:

Way back (I remember it being 1975 or 1976) BBC2 showed a documentary about a guy called Smith - a prosperous retired gentleman, I'd say - who decided he wanted to build and fly an airship, and how he went about doing it. It was a pretty ramshackle craft, as I recall, but it definitely got off the ground.

I've never seen the programme since, and as far as I know it never made it onto Discovery Wings, but does anyone else remember the programme, and - if it ever got in a repeat in the VCR age - does anyone have a copy of it? There's scarcely a reference to it on the internet, and I'm beginning to think I'm the only person who ever watched it!