Newcastle United were informed last night that they have a fight on their hands to appoint Harry Redknapp as Sam Allardyce’s successor, with Portsmouth signalling their determination to retain the services of their “valued” manager. While Newcastle are confident about securing their first-choice target — an official approach is expected this morning — their pursuit of Redknapp promises to be difficult and expensive.

Portsmouth say that Newcastle’s interest in the 60-year-old manager is yet to be transformed into official contact — “the club have received no approaches,” they said — nor would they welcome it. Redknapp signed a new contract at Fratton Park in October, stretching until 2011, so at best Newcastle would be liable for a compensation package of about £8 million, though that would not be prohibitive for Mike Ashley, the billionaire owner.

Portsmouth, who described Newcastle’s interest as “unhelpful”, do not wish to contemplate that, although their resistance may not be unbreakable. “Harry is the manager we see going forward,” Peter Storrie, their chief executive, said. “But obviously if Harry says he want to leave, it’s a different scenario. I sincerely hope we never get into that situation.”

Redknapp also denied receiving overtures from Newcastle, but associates have spoken of his eagerness to work at St James’ Park, even if his family are reluctant to move from the South Coast. Newcastle made no further public comment, although silence did not mean inactivity. Beyond the commitment to hiring a man of “experience” — effectively ruling out Alan Shearer — they have placed no restrictions on their search. No other members of staff have been asked to leave.

Mark Hughes, the Blackburn Rovers manager, has been named by Newcastle’s Evening Chronicle as a rival to Redknapp, while the betting also shortened on Kevin Keegan making an emotional return to Gallowgate. Bill Kenwright, the Everton chairman, has spoken to Ashley and received assurances that there is “no truth” in speculation linking David Moyes to the Newcastle job.

If there is bemusement among fans that Redknapp should figure so prominently on Newcastle’s shortlist — the likes of Shearer and José Mourinho probably would lead any popular vote — there was a reassuring message yesterday from Paul Kemsley, one of Ashley’s most trusted confidants and a man with close links to Redknapp — the pair had a joint interest in a racehorse named Sunshine Ray. “I will not comment on [whether] anyone is lined up, but I know Mike well enough to know that he does not make decisions rashly,” Kemsley, who attempted to take Redknapp to White Hart Lane during his spell as vice-chairman of Tottenham Hotspur, said.

“He is a very considered guy. He will know where he is going with this. He will stick with the plan and deliver what he believes will please the Newcastle fans.

“Mike isn’t a loser. This is a guy who made a billion [pounds] just after his 41st birthday. He is one of the most successful entrepreneurs this country has ever delivered. I absolutely know that if Mike is given the time, he will deliver the good-quality attacking football that the fans want. He has a plan. If I was a Newcastle fan, I would be very excited. That man will deliver. There will be more money.