Factbox: What next after Britain backs Heathrow expansion?

By Sarah Young LONDON (Reuters) - The British government gave Heathrow the green light on Tuesday to build a third runway, which will be the first new full-length runway since the 1940s in southeast England, the economic engine of Britain. Heathrow has said the new runway will be open for flights by 2025, but building is not expected to start until 2021, with the project subject to a parliamentary vote and years of consultation processes and planning approvals. Below are a summary of what will happen next and reactions to the decision: PARLIAMENT The decision will be subject to a public consultation while the government starts work on a National Policy Statement which will be put to parliament for a vote in late 2017 or early 2018. A majority of lawmakers back expanding Heathrow, according to a poll of 150 MPs carried out by ComRes for Heathrow in August, but the project has some high-profile political opponents including Foreign Secretary Boris Johnson and Education Secretary Justine Greening. Zac Goldsmith, a lawmaker from the ruling Conservative Party representing the Richmond Park and North Kingston area which is under the flight path, has in the past said he would quit if Heathrow is given the go-ahead. Prime Minister Theresa May has already taken the rare step of promising colleagues who oppose the decision that they would be allowed to air their views in public. HEATHROW AIRPORT The airport is expected to start its own public consultation process on the expansion plan next summer, while also working on a Development Consent Order, part of the planning process for an infrastructure project of such national significance. Under the airport's envisaged timetable, consent would be granted in 2021, after which construction could start. OPPOSITION Five local councils around Heathrow including Maidenhead, the area May represents, plus Richmond and Wandsworth, have hired law firm Harrison Grant to fight Heathrow expansion. Other opposition groups have also said they are likely to consider legal action against a new runway at Heathrow. Environmental group Plane Stupid, which opposes any expansion of air traffic in the UK, staged a protest in Westminster on Tuesday. In 2015, the group disrupted flights at Heathrow after members cut through a fence and chained themselves together on the runway. FINANCING Heathrow, owned by Spanish infrastructure company Ferrovial, Qatar Holding, China Investment Corp and other investors, has said it will fund the cost of building the new runway. Airlines like IAG, the owner of British Airways which is Heathrow's biggest airline, have worried that the airport will charge them higher fees to fund the new runway. The government said on Tuesday that the UK aviation regulator would work with Heathrow and the airlines to ensure the new runway is affordable and keeps landing charges paid by airlines close to current levels, a plan welcomed by IAG. SURFACE COSTS Government money is likely to be needed to fund changes required to improve road and rail access for Heathrow. These costs were estimated by the 2015 Airports Commission at 5 billion pounds, while Heathrow estimates they will cost around 2 billion pounds. BUILDING WORK Heathrow Airport in March named four companies to help it further develop its expansion plan. Construction advice, design and project management will be provided by British engineering firm Arup, U.S.-headquartered engineer CH2M, British construction firm MACE and construction and project management firm Turner & Townsend. Contracts for future construction work will be awarded later on in the process. Heathrow's last major expansion project, Terminal 5, which opened in 2008, was worked on by engineers Arup and Mott MacDonald, with Laing O'Rourke responsible for the construction. Companies including Bechtel, AECOM, CH2M Hill, Arup and WS Atkins are working on Crossrail, a new London rail route which is currently Britain's biggest infrastructure project. REACTIONS TO THE HEATHROW DECISION Mark Boleat, policy chairman at the City of London Corporation, welcomed the announcement: "After much indecision over this critical element of the UK's infrastructure, we finally have a positive outcome which will greatly benefit business." Richard Robinson, chief executive of civil infrastructure, Europe, Middle East, India and Africa at AECOM: "This is a welcome fillip for the UK's infrastructure sector and the businesses that rely on it. The focus now must be on accelerating delivery." Philippa Oldham, Head of Transport and Manufacturing at the Institution of Mechanical Engineers: "This is so near and yet so far. The year of consultation means yet more uncertainty, at a time when we need to be definite about our industrial strategy." William Lowe, Director of Heathrow Hub, the organization behind the rival plan to extend one of Heathrow's runways: "We are relieved that the government has made the correct decision in terms of location. Heathrow is where the airlines want to be; it's where the demand is." Carolyn McCall, CEO of easyJet, Europe's no.2 budget airline which currently flies from Gatwick and not Heathrow: "This is good news for UK consumers and businesses and will help ensure that the UK is better connected to the rest of the world. With the right charging structure and the right infrastructure for our efficient model, easyJet plans to operate from Heathrow, in addition to our existing London bases, providing new routes and lower fares to customers." Michael O'Leary, CEO of Ryanair, Europe's biggest budget airline: "Approving a third runway at Heathrow over Gatwick is not the way forward. London now benefits from 3 competing airports, and 3 large competing airlines (BA, easyJet and Ryanair) and the best way to deliver additional runways in a timely and cost efficient manner is to approve 3 additional runways, one each at Heathrow, Gatwick and Stansted." (Reporting by Sarah Young; editing by Giles Elgood)