* Britain plans to offer transferable tax history
* Move will help with decommissioning burden (Adds analyst comment)
LONDON, Nov 22 (Reuters) - Britain plans to introduce tax changes to oil and gas companies operating in the North Sea, finance minister Philip Hammond said on Wednesday, in a bid to spur investment in the ageing basin.
Presenting Britain's budget for next year, Hammond said that starting November 2018, tax history for oil and gas fields in the North Sea would be transferable from seller to buyer.
That will allow buyers to benefit from larger tax relief when fields reach the end of their life and require dismantling, known as decommissioning.
Britain's Oil and Gas Authority forecasts that North Sea oil and gas operators will spend almost 60 billion pounds ($78 billion) on decommissioning wells, platforms, pipelines and other infrastructure between now and the 2050s.
Government relief covers about 40 percent of the total costs.
Legislation on the tax relief will be published in spring 2018 with the aim of making transferrable tax histories available from Nov. 1, 2018, according to the proposed budget.
The North Sea has seen a flurry of deals in recent months, including Royal Dutch Shell's $3.8 billion sale of assets to private-equity backed Chrysaor, as longstanding operators make way for a new generation of smaller firms focussed on squeezing more profit from old assets.
Decommissioning remains a sticking point in many of the negotiations as the original operator of a North Sea field retains ultimate responsibility for its dismantling.
As a result, companies such as Shell or BP agreed in some cases to share part of future decommissioning liabilities in deals in recent years.
Amjad Bseisu, chief executive of North Sea-focussed company Enquest, which specialises in extending the life of ageing assets, welcomed the government's announcement.
"It makes sense for such tax losses to be transferable with the assets as it increases the efficiency with which assets can change hands in the North Sea it is another tool in the deal toolkit," said Bseisu.
Enquest this year acquired stakes in several North Sea fields and assets from BP for $85 million under which BP agreed to pay part of the decommissioning costs.
The government said it would also launch a technical consultation on allowing a petroleum revenue tax deduction for decommissioning costs incurred by a previous licence holder.
Philip Whittaker, energy director at The Boston Consulting Group, said the tax relief underscored the importance of decommissioning in the North Sea in dealmaking.
"The impact and value of the measures will be very deal-specific, but it represents another lever in the commercial toolbox that existing operators and new entrants can apply to help deals progress," he told Reuters. (Reporting by Ron Bousso; Editing by Edmund Blair and Mark Potter)