Wragge & Co is offering clients a package to do all their annual legal work for a set fee.
Wragges' managing partner Quentin Poole says the deal would save both the firm and the client money.
He claims the savings would derive from a cut administration costs for both sides, when the yearly fees can be estimated reasonably accurately.
Poole says the deal would particularly suit public sector clients.
He says: “If you have a business that is very transaction-oriented and that in one year might spend £100,000 and in another year might spend a million, then it wouldn't work.
“But there are a lot of clients around, who, because of the nature of their business, can predict a reasonably constant amount of legal work.
“The public sector is an example of that.”
He says that for £1m of work, a local authority might spend £100,000 on dealing with matters like tendering and checking bills.
And a law firm will spend a similar figure submitting for work and billing item by item, he says.
“Instead of it costing the local authority £1.1m and the law firm £1.1m, why don't they just split it down the middle so they both save £100,000?” he says.
“And if one or other party got their figures horribly wrong, if the trust and confidence was right, you'd have a conversation.”
Poole says no clients have taken up the offer so far, because the public sector is “worried about getting ripped off”.
“This is a highly commercial deal, and it may be we'll find it easier to sell to the private sector even though it is better suited to the public sector,” he says.