It was meant to be a touching tribute from Brighton’s first Green MP to her new constituents.

But Caroline Lucas’ decision to affirm her allegiance to the Queen clutching a pebble from Brighton beach brought her close to a brush with the law, The Argus can reveal.

Taking stones and shells, which form an integral part of the city’s sea defences, from the beach is illegal Brighton and Hove City Council has confirmed.

It means the Brighton Pavilion MP, she joined dozens of new MPs in fulfilling their legal requirement to swear oaths or affirm allegiances in the Commons chamber on Thursday, may have broken the law on her first day as a law maker.

Fortunately for Dr Lucas, who says she has since returned the pebble to its rightful place, the authorities are unlikely to pursue the matter.

A city council spokesman said: “Technically it’s illegal to remove pebbles from Brighton beach but while our seafront officers are instructed to report anyone taking large quantities of pebbles to the police they are unlikely to report visitors taking a single pebble home to remember their visit.”

In 2003 the council held an amnesty, promising not to prosecute anyone who returned stones, shells or larger items to Brighton beach.

The council spokesman added: “Visitors to Brighton and Hove will always want to take a memento home with them and for some this is a pebble or sea shell from the beach and on the face of it this seems relatively harmless. However the problem is that the city has a perpetual sea defence problem and pebbles play their part in protecting the seafront.”

Dr Lucas said yesterday: “During my affirmation I held the pebble to symbolise the fact that the concerns and interests of Brighton Pavilion will be my key priority. People can rest assured that I’ve since taken the pebble back so there is no need to worry.”