Can I exit to Laos and return to Thailand without violating my visa exemption status?

You did not enter on a Visa on arrival :/

IF you showed up here on a british passport without having bought a visa from a thai consulate before hand you would have been stamped in for free on what's known as a 30 day visa exempt entry.

Be that as it may,

If you were to go to Lao you would stamp OUT of thailand, canceling that entry stamp. <- meaning you no longer have a valid stamp to be IN thailand.

Then when you fly back in, IF you stamped into the country you would get a NEW 30 day visa exempt entry stamp and then stamp back out when you fly out

yes,, why not