Herbert Smith and McGuireWoods are set to take lead roles on a multibillion-pound lawsuit brought against former Lloyds TSB directors for allegedly misleading investors over its merger with Halifax Bank of Scotland (HBOS) in 2008.

The case will be launched in the coming weeks, dependent on funding being obtained by the claimants – shareholder group Lloyds Action Now (LAN) – with the action expected to reach trial in the next two years.

If the case proceeds, Herbert Smith is in line to act for Lloyds, with McGuireWoods dispute resolution partner Hardeep Nahal acting for LAN.

The case involves a claim by LAN that shareholders were not informed of a £25.4bn emergency Bank of England loan given to HBOS in October 2008 prior to its merger with Lloyds TSB in January 2009.

LAN claims that Lloyds' directors failed to inform shareholders that HBOS was "in such a parlous financial shape" and that the bank would have "had to close if its doors for business on 1 October 2008 had it not been for the granting of a secret loan".

The claims are being levelled against 15 current and former directors of Lloyds including former chairman Sir Victor Blank and former chief executive Eric Daniels.

LAN claims that Lloyds' shareholders have lost between £1.20 and £2.80 per share since the HBOS deal, valuing the case at between £6bn and £22bn.

In 2010 Winckworth Sherwood advised LAN on the legal action, fielding a team led by litigation head Jim Rai, with Nigel Jones QC and Paul Reed QC of Hardwicke Building instructed as counsel. However, both Winckworth and the Hardwicke silks have since been taken off the case.

Jeremy Cousins QC of 11 Stone Buildings is expected to be instructed by McGuireWoods if the case proceeds.

LAN currently comprises around 8,000 of Lloyds' 800,000 shareholders, a significant increase on the 500 members the group had when the case was first raised in 2010.