Partners of mid-tier firm BDO and PKF have approved the proposed merger of the two firms, which was announced in November.

The merger, which is expected to be completed by spring 2013, will see both firms operate under the BDO banner, generating an estimated UK fee income of nearly £400m, which would push them up the rankings to number six spot, slightly behind nearest rival Grant Thornton, which reported June 2012 year-end revenues of £417m.

The new UK firm will be a member of BDO International.

Simon Michaels, managing Partner of BDO LLP, described the move as 'transformational'.

'We're delighted that two firms with similar cultures and a focus on client service will combine to create an even stronger entity next year. The merged business will have firm financial foundations and an ambition to grow. Both firms employ many talented people capable of delivering quality work to a range of clients, across audit, tax and advisory,' said Michaels.

PKF's managing partner, Martin Goodchild: 'Our primary focus as we move to completion will be to ensure both our clients and people benefit from the merger; they will be working with a resilient partnership leading from a position of strength and with a client service ethic at its heart.'