From the Federation of British Historic Vehicle Clubs web site:
Are thefts of historic vehicles on the increase?
A couple of years ago, there was a sense that thefts of old vehicles, particularly of higher performance cars of the 1960s, was on the increase. We set up a system to enable victims to report their losses to see if there was any pattern. Over a period of about a year, we heard of fewer than 10 instances of theft, there was no pattern and we heard nothing more. Then this week, two reports: first, a 1965 Austin Healey 3000 (red over black, blue seats - leather in front, vinyl in back) stolen in West London in March and then a full collection of early motorcycles stolen in Gloucestershire early in April.
If similar thefts occur within one police region, it is likely the police will notice a pattern and investigate accordingly. If similar thefts occur in different areas, it is unlikely that the pattern will emerge for some considerable time - and that is why FBHVC asks to be informed of historic vehicle thefts: we can't do anything with any one individual case, but we might spot a pattern before the police are able to do so.