Christmas travellers should plan journeys carefully and prepare for restrictions on passenger numbers, Transport Secretary Grant Shapps says.
He said there will be more freedom to visit loved ones next month as all four UK nations move “very close” to agreeing rules on festive gatherings.
Talks between the nations to discuss the rules are taking place.
The first ministers of Wales and Scotland both said they were hopeful a “common” framework could be agreed.
Speaking ahead of the meeting of the UK government’s emergency committee Cobra, Welsh First Minister Mark Drakeford said he was “very hopeful” of progress being made – but cautioned any extra freedoms would not be an instruction to do “risky things”.
Scotland’s First Minister Nicola Sturgeon also stressed any changes would be “temporary” and “limited” and the Scottish government would “continue to ask people to err on the side of caution”.
She said that the “details” may differ “to reflect different circumstances in each nation”, such as what the definition of a “household” might be.
Referring to domestic travel during the festive period, Mr Shapps said the government would “have to ask people to take a close look at any proposed journeys and routes they are taking” amid pressure on services.
He urged those travelling on public transport to pre-book tickets as the capacity of services remains reduced to allow for social distancing and as a result of staff self-isolating.
Mr Shapps also highlighted Network Rail’s plans for a series of upgrades and routine maintenance across Britain between 23 December to 4 January.
He told BBC Radio 4’s Today programme: “I would appeal to people to think very carefully about their travel plans and consider where they are going to travel and look at the various alternatives available.”
Mr Shapps added that people who live in areas placed in the highest tier of restrictions in England should avoid leaving their region entirely.
“We are dissuading people travelling around generally from the very high tier areas,” he said.
One option discussed by the four UK nations would allow three households to meet up for up to five days next month, BBC deputy political editor Vicki Young has reported.
Mr Shapps said confirmation of the exact rules would come by Thursday – when people find out which tier their local area will be in – or potentially before then.
‘No Christmas truce’
It comes after Prime Minister Boris Johnson confirmed tougher tier curbs once England’s lockdown ends.
Gyms and non-essential shops in all parts of England will be allowed to reopen from 2 December under a strengthened three-tiered system.
Areas will not find out which tier they are in until Thursday – and the decision will be based on a number of factors including case numbers, the reproduction rate – or R number – and pressure on local NHS services.
At a Downing Street news conference on Monday to outline a “Covid-19 winter plan”, Mr Johnson admitted Christmas this year would be very different to normal.
“I can’t say that Christmas will be normal this year, but in a period of adversity time spent with loved ones is even more precious for people of all faiths and none,” he said.
“We all want some kind of Christmas; we need it; we certainly feel we deserve it.
“But this virus obviously is not going to grant a Christmas truce… and families will need to make a careful judgement about the risks of visiting elderly relatives.”
Meanwhile, Mr Shapps announced people arriving in England from many countries will be soon able to reduce their quarantine period by more than half if they pay for a coronavirus test after five days.
The rules will come into force from 15 December and the tests from private firms will cost between £65 and £120.
Elsewhere, Health Secretary Matt Hancock told MPs the UK’s new mass testing capacity could be used after the pandemic to diagnose a wider range of illnesses.
He said a British culture of “soldiering on” and going to work despite having symptoms of illnesses, including flu, “should change”.
“In fact, I want to have a change in the British way of doing things where ‘if in doubt, get a test’ doesn’t just refer to coronavirus, but refers to any illness you might have,” he said.
A further 15,450 confirmed coronavirus cases were reported in the UK on Monday, with another 206 deaths within 28 days of a positive test recorded.
Latest figures from the Office for National Statistics showed the total number of deaths occurring in the UK is nearly a fifth above normal levels.