Cross-border litigation with UK lawyers and non-lawyers (and others) is becoming easier for US lawyers. An example arises from ABA Formal Opinion 464. An ABA Journal article from November 2013 provides background and color.
The bottom line is that the opinion allows cross-border fee sharing with nonlawyers, in some circumstances. It states:
“In summary, a division of a legal fee by a lawyer or law firm in a Model Rules jurisdiction with a lawyer or law firm in another jurisdiction that permits the sharing of legal fees with nonlawyers does not violate Model Rule 5.4(a) simply because a nonlawyer could ultimately receive some portion of the fee under the applicable law of the other jurisdiction.”
The opinion framed the issue as follows:
“This opinion considers whether a lawyer subject to the Model Rules may divide a legal fee with another lawyer or law firm practicing in a jurisdiction where the other lawyer or law firm might eventually distribute some portion of that fee to a nonlawyer. In contemporary practice, lawyers routinely work with lawyers from other law firms, including lawyers and law firms in other jurisdictions, to represent clients in particular matters. The August 2012 amendments to the Model Rules expressly recognize these common arrangements. New Comment  to Model Rule 1.1 explains that a lawyer may retain or contract with other lawyers outside the lawyer’s own firm to provide or assist in the provision of legal services to a client anddescribes how a lawyer should approach these relationships with both the client and the other lawyers.
Sometimes the other lawyers with whom a lawyer may work are admitted and practice in other jurisdictions, both within and outside the United States, a situation that has become morecommon with the growth of national and international commerce. Those other jurisdictions may have professional conduct rules identical or similar to Model Rules 1.5(e) and 5.4(a), which dealwith the allocation of legal fees among lawyers and nonlawyers. But some jurisdictions, like the District of Columbia and the United Kingdom, have rules that differ significantly from Model.”