The Irish millionaires JP McManus and John Magnier are expected to buy more shares in Manchester United next week so they can become the largest shareholders in the club, leading to increased speculation they are preparing for a complete takeover.

Football and finance sources claimed yesterday that McManus and Magnier will increase their shareholding in United from the current 6.77 per cent to just over 10 per cent and plan to spend another £20 million sterling increasing their stake in the club.

News that the Irish duo had already spent £30 million sterling to take their shareholding in United up to 6.77 per cent caught the club and the football world by surprise on Wednesday.

The move is rumoured to have strengthened the position of club manager Alex Ferguson, who is close friends with McManus and Magnier, in his long-running dispute with the United board and their chairman Martin Edwards.

It is believed that McManus and Magnier will buy more shares through their Cubic Expression Company, which is registered in the British Virgin Islands, in an attempt to become more powerful within Old Trafford than Rupert Murdoch's BSkyB, which owns 9.99 per cent of the club.

News of the increased shareholding was welcomed yesterday by Shareholders United, the powerful group of independent United shareholders who were instrumental in preventing the club being taken over by BSkyB. In total, 19.78 per cent of United shares are owned by individuals.

McManus and Magnier are expected to meet representatives of the group over the coming weeks and a spokesman, Oliver Houston, said yesterday that "lines of communication" had already been opened with the Irish duo.

Houston said: "We are relieved to find out that Cubic Expression are a business coalition of well-known United fans and not a corporate predator. We hope that we have interests in common and that we will be able to work together in the future for the benefit of all supporters of the football club. We think we could team up with them on a whole range of issues."

However, while McManus and Magnier publicly declared their involvement in the Cubic Expression Company through a statement yesterday, mystery still surrounds who else might be involved in the United venture.

Speculation has been rife that Ferguson could also be involved in the Cubic Expression Company and could become chairman if a takeover of the club was successful. However, a spokesman for McManus and Magnier denied that anybody else apart from the duo are involved in the United venture, pointing out that Cubic Expression is owned jointly by the two.The spokesman also denied that the Irish duo had long-term ambitions to takeover United.

"They are long-term fans who see this as a good investment and nothing else," he said. So far, Magnier and McManus have not approached the former chief executive Martin Edwards, now chairman of the football club board, with a view to buying his 6 per cent stake and have not requested a seat on the plc board although the situation could change if they increase their shareholding in the club.

Yesterday Manchester United's shares rose 0.5p to 173p, valuing the club at £449 million.

Officials of Manchester United, in Bangkok at the beginning of a 12-day tour of Thailand, said yesterday they had received assurances from Ferguson he was not set on a course of action that would eventually see him emerge as the most powerful off-the-pitch figure at Old Trafford.

United's officials pointed out that neither McManus nor Magnier have bought their way on to the board with their latest share dealing and also focused on the statement from the two men that said their renewed investment in United was merely a financial matter. Now United appear to have received further assurances from Ferguson that he is not party to any potential enlargement of McManus and Magnier's involvement in the club.

Despite the current denials however, Ferguson has been enthusiastic about his Irish friends interest in United in the past.

Two summers ago, when then chairman Edwards was trying to sale shares in United, Ferguson was very keen that Edwards sell them to McManus and associates.

Meanwhile, Gaizka Mendieta yesterday became the most expensive Spanish player ever as Lazio made their first big summer transfer splash.

The deposed Italian champions agreed a #30 million fee with Valencia for the international midfielder, who will complete the move pending a medical today.

Lazio have pinpointed the man who helped the Spaniards to the last two Champions League finals as the key cog in their challenge to dethrone city rivals Roma as Italy's leading team.