On one hand, vintage Britmobiles do have a reputation for not burning gasoline during a significant portion of their lives... They're perfect for someone who really likes working on cars as a hobby and has alternative methods of transportation.
On the other hand, modern catalytic convertors are cheap and quite unrestrictive. Pop in a generic universal model, and it'll eat a shocking portion of unburnt hydrocarbons, even on old carburated cars. Not to mention, it'll deodorize the exhaust. We're all getting spoiled with these new cars, old cars without catalytic convertors stink!