Roger Federer says he \"has the fire back\" as he prepares for a tilt at a record-breaking sixth ATP World Tour Finals title.Federer is the defending champion at the O2 Arena in London and, ahead of his tournament opener against Jo-Wilfried Tsonga on Sunday, the Swiss great is delighted with how his preparations have gone.A six-week break after the US Open has been followed by back-to-back successes in Basel and Paris and he arrives in London as the tournament favourite.Speaking at a charity gala which raised more than £400,000 which will go towards a new heart and lung centre at London\'s Great Ormond Street Children\'s Hospital, Federer told Sky Sports: \"It\'s always nice being back in London and to a place or championship where I\'ve played so well in the past.\"I\'ve had a great last two weeks and before that a lot of time off for family and practice and getting some energy and some fire back.\"I\'m very happy how things are going and I couldn\'t be more happy to be qualified (for the Finals) again.\"British hopes lie with Andy Murray, who has been in good form himself of late, winning three tournaments in a row during the tour\'s Asian swing.However, Murray, beaten in the semi-finals last year, does not expect things to be easy.\"Every match is nails, it\'s really tough here,\" he said.\"If I play well I\'ll give myself a chance, but all the guys that are here have all played great tennis this year and it\'s going to be tough.\"Murray will face world number one Novak Djokovic in the group stages at the O2 and the Serb is relishing playing in front of 17,000 fans again.He said: \"I think English people have a lot of appreciation for tennis and a lot of knowledge because of Wimbledon.\"It\'s always a packed staidum and full house and for us players it\'s always a pleasure to be part of such an event.\"Rafael Nadal echoed those sentiments, adding: \"The atmosphere in the O2 Arena and the court is fantastic.\"You can be tired (at the end of the season) but when you are there and go on court and see the full crowd it\'s a very, very high motivation.