British newspaper sunday Times reports two of the shareholders in Britain's biggest ports operator, Associated British Ports Holdings Ltd (ABP), have put a third of the business up for sale.

The auction by Goldman Sachs Infrastructure Partners and the Prudential's infrastructure arm Infracapital is expected to put a value of more than £4 billion on Associated British Ports.

ABP owns and operates 21 ports in the United Kingdom, including the Humber ports and Southampton. The firm manages around 25 per cent of the UK's sea-borne trade.

The current shareholder structure of ABP is the following:

• Borealis Infrastructure, the infrastructure arm of Canada's pension fund Ontario Municipal Employees Retirement System (33 %);
• Singapore sovereign wealth fund GIC (33%);
• Goldman Sachs Infrastructure Partners (23 %); and
• Prudential's infrastructure arm, Infracapital (10 %).

According to the source, GIC and Borealis have the first right of refusal if other shareholders sell. And they are believed to have settled on acquiring about another 7% each, giving them a 40 % stake each. This would leave a 19 % stake up for grabs for other potential investors.

ABP was taken private in 2006 for £2.8 billion by the consortium mentioned above. At that moment, ABP was de-listed from the London Stock Exchange.

In 2013 ABP had revenue of £503.8 million (+6.8 % compared to 2012) and an underlying operating profit of £250 million (+8.8 % compared to 2012). Traffic figures also grew at around 4 % during 2013.