British Airways is running flights as normal from Heathrow and Gatwick after averting a strike by cabin crew.
The deal came after a marathon weekend of talks
After lengthy talks, BA and the Transport and General Workers Union (T&G) reached an agreement on Monday.
However, many BA flights are expected to take off almost empty as thousands of passengers have already made alternative travel arrangements.
BA denied it had cut fares to attract new customers but is offering return tickets to Paris for less than £80.
Since many passengers have already made alternative plans, BA has many empty seats to fill on Tuesday and Wednesday.
The airline said its "full range" of fares were available but denied that it was slashing its ticket prices.
"These are our normal great value fares that are available year round" said a BA spokesperson.
Heathrow to Paris - £39
Gatwick to Madrid - £37
Heathrow to Geneva - £44
Heathrow to New York - £248
Heathrow to Miami - £308
Heathrow to Dubai - £288
European fares are one-way, others are returns. All prices include taxes
However, the cheapest tickets that usually sell six months in advance were available again for flights leaving imminently.
"Passengers can book online for flights leaving today", said BA.
Examples of cheap fares include one-way tickets from Heathrow to Paris for £39 and Gatwick to Madrid for £37, with returns costing twice that.
Available long haul fares include a return from Heathrow to New York for £248.
However, the move has met with anger from certain passengers whose travel plans have already been disrupted.
While flights have all been reinstated, some flights from Heathrow have limited catering, and passengers are being given vouchers to buy food instead.
All catering on Gatwick flights is running as normal.
In separate news, a strike by Italian air traffic controllers means that there are restrictions on flights to Italy, affecting BA flights as well as other airlines, a BA spokesperson said.
Pay, pensions and the management of sickness absence were at the heart of the planned two-day strike, called off on Monday.
The agreement, reached after more than 120 hours of talks, also means two potential 72-hour strikes earmarked for February have also been cancelled.
BA chief executive Willie Walsh said he was "really pleased" with the conclusion to the talks while T&G general secretary Tony Woodley said it was "a fresh start".
But Mr Walsh rejected the notion that BA had "caved in" to the union.
Despite the resolution, there are fears over the impact of the dispute on the airline's reputation.
One BA customer, Jenny Lainchbury, said she had "always flown with BA" but now didn't know if she would "risk flying with the airline again".
She said the experience was stressful because she couldn't get through to anyone at BA by phone.
If the strike had gone ahead it would have threatened her daughter's wedding plans and cost thousands, she said.
Aviation consultant and former BA manager Laurie Price said "damage" had been done.
"One thing we need to remember is that the vast majority of BA's serious revenue comes from a very core group of very frequent flyers," he said.