The 24-year-old Manchester City midfielder is understood to have put pen to paper on a five-year deal at St James' Park after the Magpies fended off competition from West Ham to clinch his £5.5million signing.

Barton's capture came after Sam Allardyce beat Hammers boss Alan Curbishley to the punch and, during talks at the club's Darsley Park training headquarters this afternoon, persuaded him he could fulfil his potential at Newcastle.

With agent Willie McKay conducting negotiations with chairman Freddy Shepherd down the road at St James' Park, the player headed off for a medical and was then ready to return home to mull over the offer.

However, it is understood he was so impressed with what he saw and heard that he turned around and went straight back to the stadium to sign a deal which is thought to amount to around £70,000 a week.

Barton's capture is likely to have a knock-on effect for the Hammers, who should now be able to complete their own move for Newcastle skipper Scott Parker.

That deal has been on ice for several days with Allardyce unwilling to sanction it until he had a ready-made replacement safely on board.

The new manager has only been back at his desk for two days following a short break, and has wasted little time in pushing ahead with his rebuilding plans.

Barton will arrive once again having to answer his critics after his training ground bust-up with City team-mate Ousmane Dabo, but with his pedigree in no doubt.

Allardyce will be confident of harnessing his temperament having managed the likes of El Hadji Diouf and Nicolas Anelka during his time at Bolton, and that will be important with the Magpies having found themselves in the headlines for the wrong reasons on too many occasions in recent years.

Tonight's development came after an eventful day on Tyneside when it also emerged that Middlesbrough striker Mark Viduka has agreed in principle to join the club.

The 31-year-old is expected to hold talks with Newcastle later this week with the Hammers, Portsmouth and promoted Birmingham all monitoring his situation.

Boro are also thought to be among those clubs to have registered an interest in Barton after his departure from Eastlands became inevitable.

The Teessiders, however, will be more disappointed at the potential loss of Viduka, although perhaps not surprised after seeing him presented with a series of options as his three-year contract ran down.

Allardyce's predecessor Glenn Roeder twice tried to sign the Australia international last season, and although manager Gareth Southgate remained hopeful of securing his services beyond the confines of his existing deal, he knew he could live to regret not tying him up before he was allowed to talk to other clubs.

Viduka's 19 goals last season were a major factor in Boro's successful fight to drag themselves away from the drop zone, and in all, he found the back of the net on 42 occasions in 100 appearances following his £4.5million move from Leeds in July, 2004.

His capture would see Newcastle replace the physical presence and hold-up play they lost with Alan Shearer's retirement last summer, and while there has been speculation over the futures of Michael Owen and Obafemi Martins, Allardyce would be more than happy to go into the new campaign with that trio and the fit-again Shola Ameobi competing to lead the line.

With out-of-contract Bolton defender Tal Ben Haim and Paris St Germain's Czech international defender David Rozehnal also in his sights, the manager is intent on making an early impact.

His transfer dealings are being carried out against the backdrop of the battle for control in the club's boardroom with Shepherd still at the helm despite his health problems.

However, would-be owner Mike Ashley is expected to formalise his 100p-per-share offer to the club's shareholders later this week.

The offer document is due to be sent out within days with Ashley hoping to clinch a complete £133.1million buy-out having already acquired a 41.6% stake at a cost of £55million.