The street artist Banksy has withdrawn an offer to send a limited edition print of a new piece to voters who shunned Conservative general election candidates in and around his home city of Bristol.

Banksy’s stunt had attracted the attention of the police, the Electoral Commission and would-be Tory MPs concerned it could skew the results in six constituencies.

Hours after Avon and Somerset police said they were investigating, a message was posted to Banksy’s website saying the “promotion” was off.

Headlined “product recall”, the message said: “I have been warned by the Electoral Commission that the free print offer will invalidate the election result. So I regret to announce this ill-conceived and legally dubious promotion has now been cancelled.”

The message was accompanied by a picture of Banksy’s famous “balloon girl” image, but with the red heart replaced by the union flag. Originally the artist said a print of this image would be available on 9 June, the day after the election, to voters in the Bristol North West, Bristol West, North Somerset, Thornbury and Yate, Kingswood, and Filton and Bradley Stoke constituencies.

It said: “Simply send in a photo of your ballot paper from polling day showing you voted against the Conservative candidate and this complimentary gift will be mailed to you.”

A “lawyer’s note” added: “This print is a souvenir piece of campaign material, it is in no way meant to influence the choices of the electorate, has no monetary value, is for amusement purposes only and is strictly not for resale. Terms and conditions to follow, postage not included.”

The offer was deeply concerning to Tory candidates. In places such as Thornbury and Yate the party is fighting off a strong Lib Dem challenge. In all, five of the six seats Banksy targeted were won by the Tories at the last election; Bristol West was taken by Labour and is a key Green party target this time.

On Monday, the police said they were investigating. A spokesman said: “We’ve received a number of complaints about an offer of a free Banksy print to people living in six Bristol constituencies in exchange for them voting in a certain way in the forthcoming election and we can confirm we’re investigating the offer.

Statement in relation to the offer of a free #Banksy print in exchange for people voting a certain way in the forthcoming general election. pic.twitter.com/XtV5T0Qnbn — Avon&Somerset Police (@ASPolice) June 5, 2017

“It is a criminal offence under the Representation of People Act 1983 for any voter to accept or agree to accept a gift or similar in return for voting or refraining from voting. Any person participating in an offer to receive a gift is at risk of being prosecuted.”

A spokesperson for the Electoral Commission said: “The law in this area is complex. Given the risk that someone taking a photo inside a polling station may be in breach of the law, whether intentionally or not, the commission’s advice is against taking any photos inside polling stations.

“A person is guilty of bribery if they directly or indirectly give any money or procure any office to or for any voter, in order to induce that voter to vote or not. It is for the relevant police force to investigate any allegations that bribery may have taken place.”

The charity Crimestoppers has been warning voters to be wary of electoral fraud during the election, saying on its website: “It’s illegal to offer money or gifts to voters, directly or indirectly, to get someone to vote a certain way, or not to vote at all.”

Banksy fans could have found themselves at risk of breaching election secrecy laws by taking pictures of a ballot paper. In 2016, the Electoral Commission issued a stern warning about taking voting-booth selfies before the EU referendum.