The Portsmouth defender is expected to formally sign a contract in the next couple of days.

Much of the £17million fee will be written off because of money still owed by Pompey after Peter Crouch’s move to Fratton Park last summer.

Chelsea tried to take their former player back to Stamford Bridge but Benitez was always confident the England international would choose Anfield – even if it was at a premium.

“Sometimes you have to spend a little bit more,” said the Liverpool manager. “You can’t compete in the top four of the Premier League unless you spend some money.

“We were looking for a player of quality and also somebody who is British because of the new Champions League rules. Glen Johnson fits both categories.”

Benitez is confident he will make other signings, although he may spend more of his time trying to hang on to likes of Xabi Alonso, Alvaro Arbeloa and Mascherano. He said: “We have a plan. We can sign one more player if necessary, but that’s without any players leaving. “Alvaro Arbeloa has had a very good season but he has one year left on his contract.

“If he signs that will be good because we will have more competition, but if we get a good offer we will have to consider it.”

Benitez is also hoping Sebastien Leto and Andriy Voronin – who both were loaned out last season – will bring in more funds along with left-back Andrea Dossena, who could return to Italy after just one season at Anfield.

Leto is on the verge of a move to Panathinaikos after he became impatient waiting for Olympiakos, where he was on loan last season, to make a move.