Tottenham Hotspur remain interested in signing Everton midfielder Ross Barkley but are unwilling to match the £50m valuation for the England international. The 23-year-old is yet to agree an extension to his contract which expires in 2018 and is braced to leave Goodison Park this summer.

It is understood Spurs are plotting a move for Barkley but they are not ready to agree to the Toffees' asking price, according to The Sun. Raheem Sterling is currently the most expensive English player in transfer history, having joined Manchester City for £44m, but the demand being made by Ronald Koeman's side would eclipse the fee paid for the winger.

Everton have offered Barkley £100,000-a-week to stay on Merseyside and become the club's highest paid player but he has shown no willingness to remain. Six players have arrived at the club at a total cost of close to £100m and owner Farhad Moshiri could be forced into a high-profile sale to balance the books.

Mauricio Pochettino is regarded as a long-term admirer of Barkley and believes he can fit into Tottenham's philosophy, but the price being quoted by Everton is currently proving to be a major stumbling block. The north Londoners have not made a single signing during the summer transfer window but are planning to raid their English rivals to kick-start the overhaul of the squad.

Pochettino wants to improve a defence which conceded the fewest goals in the Premier League last season – just 26 in 38 matches – with the addition of England Under-21 international Alfie Mawson from Swansea City and Middlesbrough's Ben Gibson, according to The Mirror.

Mawson greatly impressed in his first full season with Swansea and, by the end of the campaign, was first choice under Paul Clement as the club avoided relegation to the Championship. Gibson, meanwhile, was part of the Boro team which did drop out of the Premier League. However, he has family ties to the club with his uncle, Steve, the incumbent chairman at the Riverside Stadium. The England defender also signed a five-year deal last year.

Daniel Levy, the Tottenham chairman, is expected to tighten the purse-strings this summer ahead of the club's move into their new stadium, so in order to finance moves for Mawson and Gibson Austrian defender Kevin Wimmer will be made available for transfer.

The 24-year-old has been unconvincing since joining Tottenham in 2015 but is valued at £20m. Southampton are interested in the centre-back while Bundesliga clubs have also enquired about his availability.