The ongoing internal conflict within the British government over the terms of the UK's exit from the European Union has deepened due to further disagreement over what kind of post-Brexit customs arrangement Britain should be pursuing with the EU.

Prime minister Theresa May is facing open defiance from many of her Cabinet ministers over the divisive issue of whether the UK should remain a member of the current European customs union, implement an equivalent partnership model, or leave the union entirely.

Mrs May and her chancellor Philip Hammond have expressed a preference for a customs partnership model, which would see the UK collecting tariffs on behalf of the EU on any imports subsequently shipped to a European destination, allowing businesses to claim rebates on goods that did not end up going to the EU.

This plan has been met with disapproval by many members of Mrs May's ruling Conservative Party, who have compiled a 30-page dossier detailing the reasons for their opposition to this model.

The document said: "The new customs partnership proposed is undeliverable in operational terms and would require a degree of regulatory alignment that would make the execution of an independent trade policy a practical impossibility."

Of concern to the prime minister is that the opponents to this plan include many members of her core Cabinet, including Brexit secretary David Davis, international trade secretary Liam Fox and foreign secretary Boris Johnson. The balance has tipped further against Mrs May in recent days following the resignation of home secretary Amber Rudd, who supported the customs partnership policy, while her successor Sajid Javid opposes it.

The government has recently suffered a series of defeats in parliamentary votes over its Brexit policy, with customs union membership and the maintenance of an open border between Northern Ireland and the Republic of Ireland becoming recurring issues.

This latest row will heighten concerns that further rebellion within her own party could make Mrs May's premiership and slim majority untenable, creating additional disruption at a time when the UK is trying to secure a viable post-Brexit trade relationship with the EU.