06:26

Labour MPs are being told by the leadership not to support an amendment tabled by Nottingham East MP Chris Leslie, which he says would allow the UK to keep open the option of remaining in the customs union.

A briefing note sent to Labour MPs ahead of today’s debate on the EU withdrawal bill and seen by the Guardian says: “This amendment would not keep the UK in a customs union with the EU”. It says it is “not possible” to “unilaterally” remain in the customs union - or create a new customs union. It goes on:

This can only ever be party of negotiations. Labour will not therefore be supporting this amendment but do recognise the importance of ensuring our final negotiated relationship with the EU retains the benefits of the customs union.

Leslie and his backers, who include a well-organised caucus of senior MPs, including Chuka Umunna and Heidi Alexander, are keen to maintain pressure on Labour’s frontbench to adopt a clearer position on continued customs union and single market membership.

The text of new clause 13 says ministers cannot appoint an exit day from the EU, without first making “provisions that shall allow the UK to remain a member of the EU common customs tariff and common commercial policy”, to replace the relevant bits of EU law.