Labour MP Tulip Siddiq, who delayed the birth of her son to vote in parliament last week, has complained that senior Conservatives are delaying the introduction of a proxy voting system to gain a “partisan advantage”.

The MP, whose son was born by caesarean on Thursday, two days after she was wheeled through the division lobbies, said that a system of allowing sick or pregnant MPs to vote when unavoidably absent was “an issue of basic decency”.

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Despite initial indications that Siddiq would be allowed to have somebody to vote in her place a week ago, the MP was subsequently told by the Conservatives she would have to go to Westminster in person if she wanted her voted to be recorded.

Insiders said the change of heart was down to intransigence from the Conservative chief whip, Julian Smith, a point not denied by Downing Street when asked about the subject on Monday.

Theresa May’s official spokesman said proxy voting had been discussed by the prime minister in the Commons last week “and said it was under active consideration”.

But the spokesman added the government was not ready to allow such a system to be introduced because “it is important that we make sure any changes we make are done in the right way. That remains the case. It is still something we are looking at.”

Siddiq hit back, arguing that the Conservatives should act quickly. “Offering a proxy to sick or pregnant MPs is an issue of basic decency, compassion and common sense. It is sad to learn that senior politicians are actively delaying proxy voting in order to gain a partisan advantage.”

The Labour MP gave birth to a baby boy, Raphael, on Thursday by elective caesarean. She had been originally due to do so on Tuesday, but found that clashed with the Brexit vote that the government eventually lost by a record 230 votes.

MPs normally have to walk through the division lobbies in order to have their vote recorded, although if they are pregnant or ill they can be “nodded through”, which means they are counted if they can make it to the parliamentary estate.

By agreement between whips, an MP can also miss a vote and their absence not be counted against them through a system of pairing, in which a member from the other party also agrees to be away, so the absences are cancelled out.

However, an MP who is paired does not have their vote recorded, and the credibility of the system is in tatters after the Conservative chairman Brandon Lewis voted last summer in a tight Brexit vote when he was paired with Lib Dem MP Jo Swinson, who was at the time on maternity leave.

The Commons on two separate occasions in the past year has indicated that it wants a system of proxy voting introduced, allowing an MP to nominate a person to vote in their absence because they are pregnant.

John Bercow, the Speaker, last week said proxy voting should be introduced immediately, and repeatedly called the failure to do so “lamentable”.