Dublin legal firm O'Donnell Sweeney has entered an "alliance" with the well-known English firm, Eversheds, in the first such arrangement between an Irish and a British company.

In a profession that has always guarded its independence from any move to consolidate with the international legal industry, the development could put pressure to other Irish firms to make similar arrangements.

Staff in O'Donnell Sweeney were informed about the alliance at a meeting on Thursday evening. O'Donnell Sweeney's managing partner, Francis Hackett, said that no money was changing hands in the tie-up.

Mr Hackett also "definitively" ruled out the prospect of a formal merger in between the two companies in the future.

"We're not selling. It's not the model that Eversheds have adopted," he said.

O'Donnell Sweeney will carry the Eversheds brand from January. Clients' foreign requirements will be met through Eversheds' international network, Mr Hackett said. The firm will also collaborate with Eversheds in exploiting new business opportunities.

While each of the major Irish accounting practices joined the big international partnerships in the 1960s and 1970s, Irish legal firms have always resisted any overtures from all of the big international legal groups.

Such approaches are frequently made, so the alliance with O'Donnell Sweeney marks something of a coup for Eversheds.

The main reason for the reluctance of Irish firms to entertain international offers is financial.

Irish firms have always sought to protect their income from international work, one of the most lucrative practice areas. Any tie-in with a foreign firm would preclude Irish firms from taking instruction from any other firm in a partner's market,reducing their scope to generate international income.

Mr Hackett said the firm "thought carefully" about that point, but said that the alliance gave the firm the opportunity to develop its international business.

"It's timely. We're finding a lot of our clients are looking to expand into Europe and this will help us to grow with them."

With 16 partners and 150 staff, O'Donnell Sweeney has been in business since 1963. The company claims to be the seventh-largest commercial law firm in Ireland and has a big property and litigation practice.

Mr Hackett said that the company has been growing its commercial practice in the past two years. It recently acted for BT in its acquisition of Cara and for Century Homes in its acquisition by Kingspan. It also carries out work in the technology sector. Its clients include Kenmare Resources; Davy Corporate Finance; Merrion Stockbrokers, Augusta UK Commercial Property and IFG .

Mainly English-based, and with a strong presence outside London, Eversheds has 2,000 lawyers and business advisers. The talks between the two companies continued for about a year before final agreement was reached.

The deal increases Eversheds' European footprint by bringing to 13 the number of EU markets in which it has a presence. It also has offices in Malaysia, China and Qatar.

"O'Donnell Sweeney has been a preferred partner in Ireland for some time and we have established a good working relationship," said Eversheds' chairman, Alan Jenkins.

"This is an excellent opportunity to extend our presence into Ireland, whilst ensuring that clients, either based in or having business interests there, feel they are getting local expertise and relationships."