Mackesys, one of London’s biggest criminal legal aid firms, has announced its immediate closure after more than 40 years in business by means of an outspoken statement on its website.

All 27 staff members at the firm’s five offices across south-east London have been made redundant.

The statement says that chief executive Sean Smith and other staff members received official notification of closure on Monday this week through a letter signed by sole proprietor Geoff Wordsworth and delivered by insolvency practitioner Quantuma LLP.

All staff wages including bonuses and expenses will be paid in full at the end of this month.

A planned merger announced in July with east London firm SJ Law collapsed around five weeks ago, it has emerged. SJ Law managing partner Vijesh Saujani said the merger broke down halfway through due diligence checks on Mackesys. SJ Law remains in practice.

The Mackesys statement says the reason for closure is Wordsworth’s health - ‘namely the failure of two of his heart valves’ -  and stresses that the firm has not been subject to intervention by the Solicitors Regulation Authority. Wordsworth could not be contacted.

The statement goes on to dismiss as ‘utter nonsense’ rumours that the firm is involved in financial mismanagement and that staff will not be paid.

‘The decision to close the firm is a private decision made solely by Mr Wordsworth as he is entitled to do,’ it says. ‘The decision to close Mackesys came as just a big a shock to Sean and his team as it did to anyone.’

The statement adds that since becoming chief executive five months ago, self-proclaimed legal services entrepreneur Smith has returned the firm to profit and increased the number of private clients by 200%.

The statement does not give any information about what will happen to open files and what action clients should take, other than to contact Quantuma.

Figures published by the Ministry of Justice show that in 2012/13 Mackesys received just over £1.5m from criminal legal aid work.