US tech firm Cooley is on the verge of signing up the vast majority of City-based Edwards Wildman Palmer partners for its long-awaited London office launch.

However, at least two London partners are expected to stay at Edwards Wildman as the firm prepares for its $675m (£430.5m) merger with Locke Lord.

Cooley also intends to take on Edwards Wildman's existing premises at 69 Old Broad Street, according to sources familiar with the matter, while Locke Lord is planning to buy more space at its Bishopsgate office to house its new partners.

It is believed that Cooley has been negotiating the London move with Locke Lord over the past two weeks, shortly after it was announced that partners at Locke Lord and Edwards Wildman had voted through their tie-up. The combined firm, which will operate as Locke Lord Edwards, is set to go live on 10 January 2015.

It is also understood that Cooley is on the brink of securing approval from the Solicitors Regulation Authority for its office launch.

The two Edwards Wildman partners thought to be among the team staying with the merged firm are intellectual property (IP) partner John Olsen and employment partner Neil Adams. It is not clear how many fellow partners, associates or staff will accompany them.

A source at Locke Lord said: "We would have liked more partners to join us from Edwards Wildman. However we are pleased to be gaining significant technology law capability with the lawyers that are set to be joining us and we look forward to working with them."

Cooley, Locke Lord and Edwards Wildman all declined to comment.

Besides Olsen and Adams, there are 18 other partners at Edwards Wildman's City base – including one non-lawyer partner – according to its own website. It is not clear how many Cooley aims to hire although sources expect it will take on "virtually all" of the remaining partnership. The office staffs 25 associates as well as one risk and compliance director, one consultant and six trainees.

For Cooley, the discussions mark a significant step forward in its protracted plans to launch in London. The US firm began to weigh up its options in London in 2012 after it ended a non-exclusive alliance with Olswang months earlier.

Cooley is understood to have been circling Edwards Wildman's City operation for some time. The latter has been left without a management figure on the ground after London partner-in-charge Nicholas Bolter was relieved of his leadership role earlier this year. The office is managed remotely by former Edwards Wildman managing partner Walter Reed, who is based in Rhode Island.