British engineers Amec, Babcock International, and Atkins are believed to be circling nuclear decommissioning work estimated to be worth at least $5bn (£3.2bn) in Japan as a result of the Fukushima disaster.
The new Japanese government is thought to be preparing decommissioning contracts that will include Fukushima's Daiichi plant, which was overwhelmed by a tsunami in 2011, and other reactors in seismically endangered areas.
A nuclear source said bids could be invited for the clean-up work before the end of the year, with British groups in a strong position due to all the decommissioning work that has been undertaken in the UK.
US-owned Energy Solutions will also be interested.
"This is a huge opportunity," claimed the source. "Japan should start making some real progress on decommissioning now."