Senior has not played since limping out of Leeds' Challenge Cup Final defeat by Hull in August with an ankle injury but he came through a full-scale training session against the England squad yesterday.
"We're really pleased with Keith's progression. It's been very encouraging," said Great Britain's assistant coach, Jon Sharp.
"He's worked really hard over the last two weeks and has come on leaps and bounds. He's been able to take part in a full practice; he's fit and healthy and available for selection."
Martin Gleeson, who will, provided the British management are not whistling in the dark over Senior's fitness, partner him in the centres, said that his presence would be a major boost.
"I know from Super League there are not many harder centres to play against than Keith," he said.
New Zealand's key man, their scrum-half Stacey Jones trained with their squad yesterday after arriving to join them under a cloud over his fitness.
The Bradford centre, Shontayne Hape, who is in the New Zealand squad, has criticised the club's decision to release his fellow countryman, Robbie Paul, to join Huddersfield.
"I don't think that's the way to treat someone who has given so much to the club," he said.
Bradford have signed the Castleford prop, Adam Watene, as part of their rebuilding for next season. Watene is a Cook Islander and does not count on the club's overseas quota.
He played in Castleford's National League One Grand Final victory over Whitehaven and has turned down an offer to stay with the Tigers in order to join Bradford.
"It's a great opportunity for me at this stage of my career to play with a big club and I am looking forward to making a big impression," he said.
The Bulls coach, Brian Noble, said: "We have been very impressed with Adam this season and we feel he will improve in our environment. "He will be a great addition to our squad for next season."
Watene is Bradford's fifth new signing, after Chris McKenna, Marcus Bai, Stanley Gene and Terry Newton.
The World Club Challenge between the Bulls and Wests-Tigers will be staged in Britain and is likely to take place at Huddersfield on 3 February.
Leeds have added Barrie McDermott and Francis Cummins, who are both retiring as players after playing for Ireland in the European Nations Cup, to their coaching staff. The former Great Britain tourist, Graeme Hallas, who has been coaching Bradford Dudley Hill in National League Three has also been brought in.
Wales have added Bridgend's Paul Morgan to their squad for their European Nations match against Ireland in Dublin this Saturday.
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