In a statement to POLITICO, Chapman, whose party has called for a customs union with the EU, accused the government of "wasting time and money" on alternative customs models by "outsourcing the problem to a private consultancy".
The, or a, customs union is one of the main flashpoints in the debate over Britain's impending exit from the EU and Brexit campaigners are sensitive to any suggestion that Britain might stay in such an association with the bloc.
The customs union has become the latest battleground between those that want to leave Europe decisively and those who would prefer a "soft Brexit", where numerous current arrangements are retained.
The customs union sets what is known as a common external tariff, so that any goods coming into the EU are charged the same amount, no matter which country they arrive in.
The government has admitted it will be dropping one of the two formal positions on future customs arrangements with the European Union, after Amber Rudd told journalists the "final position" had not been nailed down. The EU says these red lines mean the only possible framework for future cooperation between Britain and the bloc is a trade deal.
"In light of the government's own impact assessments and the lack of progress on any new trade deals, any economic case for ruling out a customs union has collapsed", he said. It is expected that this will be replicated in today's non-binding vote in the Commons.
"There are two options which we put forward and those two options are now on the table, but as we move forward you can expect us to move forward with a single option", the spokesman told reporters.
A "customs partnership" that would involve the United Kingdom collecting the EU's tariffs on goods coming from other countries on the EU's behalf is under consideration, along with proposals for minimised checks using technology and a trusted trader scheme.
Negotiators in Brussels have rejected both possibilities as unworkable and neither option has strong domestic support.
However, when asked last month by MPs on the House of Commons European scrutiny committee which of the U.K.'s two customs proposals he preferred, Davis said: "What is the point of paying consultants to do this work and to make the decision in advance?"
The votes that count will come next month - the EU (Withdrawal) Bill is now being reviewed in the House of Lords and is due to return to Commons in May.
May and her supporters could face an embarrassing defeat in parliament if members of her own Conservative Party ally with others to press for a continuation of the customs union.
Yvette Cooper, who chairs the Home Affairs Committee, and Treasury select committee chairwoman Ms Morgan said in a joint statement: "We both believe the case for a customs union is overwhelming - for the sake of British manufacturing, global trade, smooth borders and Northern Ireland peace".
If that happens but May stays on as leader, the war of words now ongoing within the Conservative Party could explode into resignations and leadership challenges.