With no written constitution in Britain, MPs have entered Brexit's uncharted territory and have begun deploying tactics that even well-informed onlookers find baffling.

In the latest skirmish this week, opposition MPs and rebel members of Prime Minister Theresa May's Conservative Party began a campaign to amend legislation to make it harder for Britain to leave the EU in March 29 with no deal.

After successfully changing a budget bill to restrict the government's taxation powers in a "no deal" scenario, they pledged to force similar amendments to every other bill passing the House of Commons before Brexit.

The moves came after the opposition Labour Party last month used an archaic procedure, "the humble address" to the sovereign, to force the publication of legal advice relating to May's EU withdrawal deal.

When ministers tried to ignore the procedure -- a device last used regularly in the mid-19th century -- they were found in contempt of parliament.

These procedural gambits have been aided by House of Commons Speaker John Bercow, who has a history of seeking to increase MPs' powers to scrutinise the government.

On Wednesday, Bercow ripped up the rulebook to allow MPs to take further action against a "no deal" Brexit.

He allowed an amendment to a motion that precedent suggested was unamendable, demanding May set out her Plan B within three days if her Brexit deal is defeated in the Commons next week.

Labour MP Jess Phillips summed up the attitude of many lawmakers who once dismissed the intricacies of parliamentary regulations.

"I scoffed at people who talked in procedure and when I arrived here I realised that actually it is the procedures of this House and protecting them and developing them that will make our democracy considerably better," she said.

#FreeErskineMay

Alice Lilly, a senior researcher at the Institute for Government, said parliament had begun to assert itself since the 2017 election, when May lost her majority in the Commons.

A fragile government combined with the desire of MPs to have their say over Brexit had led lawmakers to act in "more innovative ways".

"We have seen almost a renaissance of focus on parliamentary procedure," she told AFP.

Parliament's legislative experts have reported increased interest from MPs in their work, while they have also started holding regular packed-out briefings for journalists.

The House of Commons is governed by a mix of rules agreed by MPs, traditions and conventions.

These are compiled in Erskine May, a book penned by a Commons clerk of the same name in the late 19th century, which is regularly updated and now runs to almost 1,000 pages.

This year it will be made available free online for the first time, after a long-running Twitter campaign, #FreeErskineMay, galvanised by the procedural wrangling over Brexit.

'Out of touch'

But the rules are open to interpretation, and this week the Speaker made clear his own power as the ultimate arbiter.

One source told the Daily Telegraph that Bercow, who is close to retirement, "is going out in a blaze of glory".

"It is kamikaze. He doesn't care," he said.

Constitutional experts in parliament said the government itself could now use procedure to wriggle out of the demand by MPs that Bercow facilitated.

But, while experts of parliamentary procedure revel in the obscure tactics being deployed, some participants are fed up.

In one debate, Conservative MP Heidi Allen said she was "hopping mad" about her fellow lawmakers' fixation on procedure instead of planning for what happens if parliament rejects May's Brexit deal.

"Do people in this house (of Commons) have any idea how out of touch the general public think we are most days?" she said.

"When are we going to start acting like public servants, doing the right thing and having the debate and getting on with it?"