Border crossings are now controlled electronically in most cases so stamps are not required. If you feel that you look like a suspicious character; keep hotel and other receipts to be able to prove when and where you have been.

But in any case, if the French border control did not care about your status, why on earth would you think that the British authorities would care how long you had been in the EU? It is not a UK problem if you exceeded the limit in the EU.