Slaughter and May will be back in the House of Lords this week as it looks to follow up its landmark tax win for client Deutsche Morgan Grenfell (DMG) with a similar win for Sempra Metals.
The Lords will hear Sempra Metals v HM Revenue & Customs for two days to decide whether foreign companies can demand compound interest when claiming back taxes.
Last week the Lords voted four to one in favour of DMG claiming back interest on Advance Corporate Tax paid since 1975, disallowing the Revenue's six-year claim limitation.
The House of Lords' decision overturned a unanimous Court of Appeal decision of Lord Justices Buxton, Rice and Parker.
The Government's tax coffers, already in danger after the loss against DMG, could be raided for further billions if Sempra Metals wins the right to claim compound, rather than simple, interest on payments.
One Essex Court QCs Laurence Rabinowitz and Ian Glick will face each other for the second time during the hearing, after going head-to-head on the DMG dispute.
Rabinowitz said about the DMG decision: "The payments go back to the 1970s. The interest on that is enormous. As I understand it, there may be billions of pounds worth of claims.
"In a way it's not great news for the taxpayer."
The Slaughters dispute resolution team includes partner Sarah Lee and senior associate Caroline Edwards, instructing Rabinowitz and 11 New Square's Francis Fitzpatrick.
The HM Revenue & Customs Solicitors Office has instructed Glick and Pump Court Tax Chambers' Rupert Baldry.