Defence Secretary Philip Hammond has insisted British operations in Afghanistan will not be affected by Nato's scaling down of joint patrols with native forces.
Nato has decided that any joint patrols and advisory work with Afghan troops smaller than battalion level will now have to be approved by regional commanders.
The temporary decision by the International Security Assistance Force (Isaf) follows a string of "green on blue" attacks by Afghan soldiers and police.
It also comes against the backdrop of an upsurge in protests linked to the anti-Islam film Innocence of Muslims and emerged hours after a suicide bomber struck in Kabul.
Amid confusion over how the order would affect soldiers on the ground and the withdrawal due in 2014, Conservative MP John Baron tabled an urgent question.
Mr Hammond therefore had to appear before MPs to give assurances about Afghan strategy for the second time in less than 24 hours, after appearing on Monday to discuss Afghan security.
He insisted that the Isaf commander in charge of the Helmand region where most UK troops are based had confirmed he is happy for British mentoring and partnering operations to continue at below battalion level.
"That means that the UK partnering and mentoring operations will continue substantially unchanged by this order," he told MPs.
However, Mr Baron - a former Army captain - said: "This announcement threatens to blow a hole in our stated exit strategy."
He added: "This announcement adds to the uncertainty as to whether Afghan forces will have the ability to keep an undefeated Taliban at bay once Nato forces have left."
Labour MP Paul Flynn was expelled from the Commons for a day after accusing defence ministers of "lying" over Afghan policy and refusing to withdraw the comment.
The restriction on troops' activities was issued by the second most senior US commander in Afghanistan, Lieutenant-General James Terry.
Senior Nato spokesman US Colonel Tim Collins said it was only a "temporary and prudent response" to the current threat of insider attacks and the mounting anger in the Muslim world over a film mocking the Prophet Mohammad.
Afghan commanders were not told of the order until a hurried meeting on Tuesday and it appeared to take Britain and other coalition members by surprise.
Mr Hammond told MPs it was issued on Sunday evening and he was informed at a meeting on Monday, after his first Commons statement.
He insisted "no particular significance was attached to it" but Sky's defence and security editor Sam Kiley said: "This is a very significant tactical shift in approach."
The decision follows the deaths of six foreign soldiers were killed over the weekend in southern Afghanistan where the Taliban have the most support.
They included two British soldiers who died when they were attacked by a man dressed as an Afghan policeman feigning injury.
Labour MP Denis MacShane said the change amounted to a reversal of the US and UK strategy but Mr Hammond said: "We have got a strategic plan. We are working towards an end to our combat operations in 2014.
"We have said all along we will take every step that we need to take to minimise the risk to our troops and that is what we are doing.
"There will be lots of measures that Isaf is taking over the next days and weeks to minimise the risk to our forces and I welcome them all."
Foreign Secretary William Hague agreed, saying: "There is no change in strategy and I think the impact of the Isaf announcement will be quite minimal on UK operations."
The Chief of Defence Staff, General Sir David Richards, told Sky News: "There is no change in strategy. How we implement the strategy is always under review."
US Defence Secretary Leon Panetta, speaking in Beijing, admitted that the US was concerned about insider attacks but insisted the plan to hand over security by 2014 was unchanged.
More than 30 such attacks have claimed the lives of 51 troops in the Nato-led coalition so far this year, sowing mistrust between the Western force and its nominal allies.
This represents a spike of more than 40% on similar incidents for the whole of last year.
Commanders believe only a quarter of the assaults are the result of infiltration by Taliban insurgents and that the remainder were caused by cultural clashes and personal grievances.
Afghanistan's defence ministry said earlier this month that it had arrested or sacked hundreds of Afghan soldiers for suspected insurgency links.
September 18: Nine Killed In Kabul Minibus Suicide Attack
September 17: Brit Soldiers Killed By Rogue Afghan Policeman
