LONDON: George Osborne has warned Theresa May that she lacks the power to force through a hard Brexit, because Parliament is now in control of the withdrawal process.

There are “increasing numbers” of Tory MPs speaking up for keeping close economic ties with the EU, including remaining in the customs union, the former Conservative Chancellor said.

“The first rule of politics is that you have got to learn to count,” said Osborne.

On the growing Conservative revolt, he said: “That is going to pose a challenge to the government, of course, but it is also going to empower Parliament.

“Last time I checked one of the principle arguments from the Brexiteers is that they wanted more parliamentary sovereignty.”

Osborne argued the economic harm from Brexit had been laid bare in this week’s leak of the secret government analysis - with the greatest damage forecast from pulling out of the EU’s economic structures.

“I question whether there is really a government majority for withdrawing from the customs union, now you have seen the economic figures from the government,” he added.

The analysis predicts staying inside the EU’s economic structures would reduce growth by 2 per cent over 15 years, compared with current projections, according to the leak, However, a no-deal Brexit, leaving Britain trading with Europe on World Trade Organisation terms, would reduce growth by 8 per cent - four times as much.

May wants a transition period which would effectively keep the UK in the single market and the customs union for about two years, to avoid a damaging “cliff edge” on Brexit day in March 2019.

But the cabinet and the Tory party is split down the middle on what happens next - with the faction led by Boris Johnson demanding a clean break from the EU at that point.

In contrast, Chancellor Philip Hammond has openly called for only “very modest” changes after Brexit, to protect the economy, and is backed by Amber Rudd, the Home Secretary, amongst others.

Meanwhile, up to 20 Tory backbenchers are ready to vote with opposition parties to keep the UK in the customs union permanently - with Labour still undecided.