Sunderland have confirmed that Darren Bent has handed in a written transfer request amid reports linking the striker with Aston Villa.Reports suggest Premier League strugglers Villa have lodged an £18m bid for the England international.The Midlands club would not confirm or deny the speculation.Bent, 26, joined the Black Cats for an initial £10m from Tottenham in August 2009 when he signed a four-year deal with the north-east club.The forward's desire to leave Sunderland will come as a shock to the club's fans and, if he does exit the club, it will leave a big void for Black Cats boss Steve Bruce to fill.Bent scored 25 times last season and has notched 11 goals in the current campaign.Eight of his goals have come in the top-flight as he has helped a Sunderland side with 26 league goals in total to sixth in the Premier League.Although he missed out on selection for the 2010 World Cup, he did grab his first international goal in September when he scored after coming on as a substitute in a 3-1 win over Switzerland.Aston Villa are presently fourth from bottom in the league as they try to move away from the relegation zone.A deal for Bent, which would break the club's transfer record, would be a show of support in manager Gerard Houllier, despite Villa's struggle for form since the Frenchman took over in September.BBC Radio 5 live football correspondent Ian Dennis said he understood that the offer from Villa was put forward towards the end of last week."I understand it was cash up front which is an enormous show of faith by Randy Lerner in Gerard Houllier," he said.Source: BBC