Yes they would, they use the manufacturers data to see what the car had when sold.
Having spoken to a mate about 5 mins ago, he's a motorbike traffic cop, he told me they routinely are asked by mib/dvla to stop cars now suspected of having different engines and not been declared, dvla are interested as if it was a 1.2 with low tax and now a 2l for example it's tax evasion also.
EVERY car that has been found to have either undeclared mods or a bigger engine than stated is taken there and then, and only given back when modified insurance cover is produced.
Plod have the number of every insurance company and they do phone them to ask about mods and insurance specifics, as I was stopped last year and they checked that my policy for my car had driving other cars on it(it did).
Most of the impetus for this is owing to them finding much larger interesting things in the process, drugs etc.
tabetha