The recent exodus of corporates away from the UK for tax reasons may not be good news for the Revenue, given the battering it has already taken this year over the taxation of non-doms, but law firms must be thanking their lucky stars.

At a time when large corporate deals are few and far between, the decision of FTSE 100 pharmaceutical company Shire to relocate to Ireland has kicked off a steady stream of work for City law firms advising other companies looking to follow suit.

Given that the deals are lengthy and expensive, and require large teams of lawyers, a handful of firms, led by Slaughter and May, seem to be doing pretty well from the mandates.

Since Shire's announcement in the spring, at least four other companies have followed its lead. Most recently, office space rental company Regus said it was moving its operations to Luxembourg, following closely in the wake of United Business Media (UBM), Henderson Group and engineering group Charter, which have all decided to shun the UK in recent months.

Each has declared they do not want to put up with the UK regime governing the taxation of overseas profits – maintaining that it is both punitive and territorial.

Slaughters has taken the lion's share of migrations to date, with the magic circle firm advising Shire, Charter and Regus on their moves. Corporate partner Andy Ryde took the lead on both Charter and Regus, assisted by significant teams from all of the firm's practice areas.

Allen & Overy (A&O) and Freshfields Bruckhaus Deringer have also picked up one relocation deal apiece. A&O is acting for longstanding client UBM on the transfer of its operations to Ireland and Jersey, while Freshfields has been advising Henderson Group on its switch to Ireland.

With marketing and communications group WPP and Brit Insurance both reviewing their tax status, the trend doesn't look too likely to end any time soon. Firms are already pointing towards a growing rank of clients who are curious about the benefits of migrating and willing to enter a lengthy due diligence period before making up their minds.

Little wonder, then, that those firms lucky enough to be involved are viewing these deals as a godsend right now.

As one magic circle partner says: "These are substantial pieces of work with quite a few issues. They are incredibly complicated and significant, especially when there is less M&A around."

While in the short term it's good news for firms, though, it may not just be the Revenue seeing its purse suffering in the longer term.

The fees may be coming in handy now, but helping some of your biggest clients move to a new country clearly comes with a few risks. Some of those involved are concerned that ongoing instructions will begin to dwindle once the client is established in its new home and starts doing deals again, when the work could go to local firms.

One top City partner warned: "In the short term, these are good instructions for a firm, but is it really good in the long run? Over time, there is a worry that the client will move away from its UK advisers."

So while Slaughters may be winning right now it could find its position at the top of the FTSE client rankings coming under threat further down the line. The trend is also unlikely to do much for London's reputation as a leading business and financial centre in the long term.

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