Officers attended the house of Rob Roberts, MP for Delyn in North Wales, after neighbours reported visitors arriving at the property.
Balloons and banners had been placed outside the home in the town of Mold to mark what is understood to have been his wife Alexandra’s 40th birthday.
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Two people were ordered to leave the property, the Daily Mirror reports.
In a post on Twitter, Mr Roberts – who was elected to the seat in December – said: “My family have been reminded of the guidance set out by the government.”
But he added that he himself was 200 miles away in London at the time. He is understood to be living in the capital during the pandemic after recently separating from his wife.
Superintendent Mark Pierce of North Wales Police said: “In response to two reports of a possible breach of Covid-19 regulations we visited an address at Ty’n y Coed, Mold [on Bank Holiday Monday].
“When we called at the property two people visiting the house left following advice and no further action was taken.”
Coronavirus restrictions mean it is currently illegal to visit other households or have other people visit you.
Mr Roberts, who came out earlier this month, is allowed to travel between London and his constituency to fulfil his duties as an MP in accordance with restriction guidelines.
The revelation of the birthday party came just a day after he announced he would not be calling for Dominic Cummings – chief advisor to Boris Johnson – to stand down after he admitted driving 260 miles from London to Durham with his wife and son while he had coronavirus.
Mr Roberts said: “I believe that he seemed to be entirely acting in the best interests of his child as a responsible husband and father…
“It is now time for us all to move on from this issue and continue to be focussed on solving this huge challenge of Covid.”
He did not address whether he believed if Mr Cummings had taken a 60 mile round trip to a well-known beauty spot on his wife’s birthday to test his eyesight.