rent a car in London to visit Bovington Tank Museum

It is quite a way to drive there and back in day. It is also a great pity that by doing this as a day trip, you are not seeing other attractions in this area - such as Salisbury Cathedral and the wonderful coastline just south of the museum at Lulwoth & Durdle Dor.
http://visit-dorset.org.uk
https://jurassiccoast.org
https://www.visitwiltshire.co.uk/salisbury

It is quite a way, but it doesn't take that long. I can do it from my home in between an hour and three quarters and two hours, though I'm the right side of London. It can be quite a pleasent drive too, eespecially if you go down the A31 and join the motorway at Winchester.

Whereabouts in London are you staying?

If you don't know London, you don't want to be driving in the city centre due to the volumes of traffic plus paying the Congestion Charge. That means spending probably an hour getting to somewhere on the outskirts of London to hire a car then a 2 + hour drive. So say 6+ hours travelling.

Some car hire companies will charge more due to your age, unfortunately.

A better option maybe to consider going by train then getting a taxi from the station to the museum.

Thank you James, Pete and Jennifer....your advice is certainly appreciated!

Tools:

http://www.nationalrail.co.uk/

https://beta.nationalexpress.com/en

Bovington Tank Museum is advertised as being within walking distance of Wool Station. It is though about 2 miles which may be a bit far, even though nearly all the way there is a pavement for pedestrians. Alternatives are the bus (3 times a day) or a taxi.