A Spanish state-owned shipbuilder will buy Belfast-based Harland & Wolff in a rescue deal that will secure all four of its shipyards and save about 1,000 jobs.

Navantia is to acquire H&W’s Belfast shipyard where the Titanic was built, as well as the Arnish and Methil yards in Scotland, and the Appledore site in Devon, ending months of uncertainty for its employees.

The exact sum paid for H&W’s assets was not immediately disclosed, but had been widely reported to be £70m, while the UK government improved a contract to build three fleet solid support (FSS) ships, which supply Royal Navy vessels with dry goods such as food.

Talks between Navantia and the UK government had been taking place since H&W went into administration in September after ministers refused to provide taxpayer-funded support to keep it going.

The Spanish shipbuilder had wanted to secure a better deal on its FSS contract, originally valued at £1.6bn, to ensure the company could “still deliver on the contract and build all three” vessels.

Navantia UK is the lead partner on the construction of the ships to support the Royal Navy’s UK carrier strike group that will be built in Belfast, Appledore and Puerto Real, near Cádiz, in Spain.

The deal is also been seen as part of the UK government’s effort to “reset” relations with the EU and forge a new security and defence pact with the bloc.

Navantia is wholly owned by the Spanish state and is involved in six European defence fund projects worth €520m (£430m) including those under the Permanent Structured Cooperation (Pesco) treaty framework.

The deal comes weeks after the Spanish economy minister, Carlos Cuerpo, met with the UK chancellor, Rachel Reeves, and the business secretary, Jonathan Reynolds, in London.

The sweetened terms of the FSS deal were not released, but it appears to push some of the financial guarantees on to Navantia. Reynolds said the change was “relatively minor given the size of that contract”.

He told reporters in Belfast it was “a far better solution than what was on the table when we initially came into office, which would have been a loan guarantee, which I believe would have lost the taxpayer all of its money and not delivered those ships and not secured the yards or the jobs”.

The Northern Ireland secretary, Hilary Benn, said the deal ensured the delivery of the FSS programme to build three Royal Navy ships. In Belfast, about 500 jobs will be protected by the deal.

Navantia, which already has a relationship with the Belfast shipyard, said the deal would “enhance UK shipbuilding, defence and offshore wind industry capabilities”.

Reynolds said the deal not only secured jobs across the country but was part of Labour’s “plan for change” to deliver high skilled production jobs.

The defence secretary, John Healey, added that the pact would keep “vital defence manufacturing in the UK” and strengthen sovereign capability to support the Royal Navy while delivering growth.