Linklaters has joined Slaughter and May at the top of the Hemscott rankings of legal advisers to FTSE 100 companies, with both firms listed as advising 25 of the UK's biggest companies.

Hemscott's Q3 rankings put the firms neck-and-neck for the first time. Slaughters has dominated the list since the rankings were first released in 2005, at which point it had 10 more FTSE 100 clients than Freshfields.

Linklaters upped its FTSE 100 count by one between May and August, with the firm listed as a new adviser to both Friends Provident and British American Tobacco, while insurance group Amlin fell into the FTSE 250.

The rest of the top five comprises Herbert Smith – which saw its FTSE 100 client count drop from 19 to 18 as it is no longer listed as an adviser to Friends Provident – Allen & Overy (A&O) and Freshfields Bruckhaus Deringer.

Freshfields gained two top-ranked clients – the London Stock Exchange Group and Wolseley – to claim fourth place alongside A&O with 17 FTSE 100 clients. Both the London Stock Exchange Group and Wolseley featured in the firm's FTSE 250 tally in May 2009.

Linklaters corporate partner Charlie Jacobs (pictured) said: "As a firm you need a good weighting of clients at the top end of the FTSE 100 where there tends to be less churn, but you also need to be alive to clients being taken over or dropping out of the 100. Over the years we have looked at a number of strategic steps to increase market share, including our sector initiative and our initial public offering practice as a way of getting new corporate clients."

Commenting on the trend for companies to cut back their legal advisers to cut costs, Freshfields London head Tim Jones said: "Every general counsel you speak to has to reduce budgets, and one of the ways of doing that is by narrowing down your roster of advisers to see whether increased volume can drive better pricing. The important marker for law firms will be to see with how many of your relationships you are the number one adviser."

Other changes in the FTSE 100 rankings include Norton Rose, which dropped two places to tenth after losing its listing against Friends Provident, while power company Drax fell into the FTSE 250.

Slaughters maintained its stronghold at the top of the FTSE 250 client rankings with 39 clients compared to second-placed Linklaters tally of 32. Ashurst, Herbert Smith and Freshfields make up the rest of the top five, with 20-24 clients each.

While there are now signs that the M&A market is starting to pick up again, law firms are still coming under pressure on fees.

Slaughter and May practice partner Paul Olney added: "For transforming deals or in life-threatening situations, clients will look for the best quality advice they can find, but in the current environment, providing good value advice is particularly important. We have to be responsive to the pressures that our clients are under."