Dutton Kit Cars and their owners
give it a wire brush and a good look over, good coat of primer and a topcoat of whatever you fancy. You'll get 16 different opinions on here of what to use :-)
I'd agree with Steve. Surface rust isn't an issue for MOT. If the metal appears to be flaking then the tester may give it a prod but as a rule 'wire brush and touch up' should see you right.
it is possible to improve the stiffness of the Dutton frame, its a fair bit of work. but can be worth it.
however surface rust is not an issue, its just a problem if its heavy enough to weaken the chassis.
If only surface rust then wire brush, zinc prime and paint, black stonechip always looks good on chassis, if you're really conscientious then waxoil over the stonechip. Most later Duttons came from the factory in red oxide but they never degreased the metal first so what ever gets painted on top just flakes off.