One of the UK’s biggest pub chains now faces a massive fine following the tragedy at the Railway Hotel, Hornchurch, East London, while former landlady Ann-Marie McSweeney and former head chef Mehmet Kaya could both go to jail.

A jury at Snaresbrook Crown Court this week found pub chain Mitchells & Butler guilty of serving up contaminated food. McSweeney, 40, and Kaya, 37, were both found guilty of perverting the cause of justice by falsifying food safety records.

The court heard that mum-of-one Della Callagher, 46, ate the contaminated festive fare – which had been cooked the day before and then warmed up – with her husband, John, on Christmas Day, 2012. Both began to suffer from vomiting, diarrhoea and stomach pain on Boxing Day, but Mrs Callagher’s condition grew progressively worse and she died in hospital on December 27.

A year-long investigation by Havering District Council found that the illness was caused by the clostridium perfringens bacteria as a result of the turkey being either not cooked or not reheated properly.

Mitchells & Butler – which owns around 1700 pubs and restaurants across the UK – is likely to be heavily fined after Judge Alastair Hammerton ordered that the company’s audited accounts for the last three years should be handed to the court..

Both McSweeney and Kaya have been warned they could go to jail. Adjourning sentencing until January 8, the judge told the pair: “I’m not ruling anything out and I can say it’s very likely that you will both receive an immediate prison sentence.”