French private investment company Ardian has hired Rothschild to sell its 49 percent stake in Britain's fifth-biggest airport, Luton, banking sources told Reuters.

Ardian and Spanish airport operator Aena, which owns the other 51 percent, bought the airport from toll operator Abertis in 2013 for 508 million euros (US$626 million).

Aena has a preferential right to buy Ardian's stake, which will be valued at more than US$400 million, the sources said.

At a management meeting with sell-side analysts this month Aena's chairman said the company is not interested in buying out Ardian's stake in Luton at any price, but sees it as an opportunity to provide an entry to a new financial partner.

A spokesman for Aena declined to comment further while Ardian declined to comment and Rothschild did not respond immediately to a request for comment.

European airports have been a lucrative business for private equity firms and pension funds over the past few years because they offer strong growth potential from increasing global travel and services such as shops, on-site hotels and car parking.

Banking sources expect infrastructure fund Global Infrastructure Partners to sell investments in Edinburgh and Gatwick airports in the coming year or two in what could be a test of investor sentiment on the eve of Britain's exit from the European Union.

Valuation Guide

Luton's valuation will help to guide potential deals for those other British airports.

London City, an airport favoured by business executives because of its proximity to London's financial districts, was sold to a pension funds consortium in 2016 at a valuation of more than 2 billion pounds (US$2.8 billion), more than 30 times core earnings and a threefold increase from the price paid by the owners a decade earlier.

In 2014 Luton gained approval for expansion of the airport and its runaway to boost capacity and attract budget airlines including Wizz Air and Easy Jet.

Almost 16 million passengers travelled to and from the airport last year, the airport's website says.

In the year to March 2017 Luton airport generated earnings before interest, tax, depreciation and amortisation (EBITDA) of 52.6 million pounds.

Ardian, which handles US$65 billion of assets across Europe, North America and Asia, recently sold a stake in industrial engineering group Fives and launched a sale of German healthcare business Riemser Pharma. Sources have said it is also considering a sale of Italian chemicals maker Italmatch. (US$1 = 0.7163 pounds) (US$1 = EUR0.8114)