The well-dressed ringleaders of Britain's biggest chequebook fraud face long jail sentences after pleading guilty to stealing around £20 million in a nationwide scam, including £5m in Golders Green.

Congo-born postman Dido Mayue-Belezika, 34, who lived in a council flat in Malden Crescent, Camden, is believed to have run the operation, stealing chequebooks at the sorting office in St George's Road, Temple Fortune, where he worked, and passing them on to accomplices who would cash them in legitimate and bogus accounts.

Mayue-Belezika and his brother-in-law Ishiaba Kasonga, 40, from Brixton, enjoyed lavish lifestyles, driving luxury cars and wearing top-of-the-range designer clothes and jewellery.

Mayue-Belezika drove a Mercedes 4x4 when not at work, while Kasonga, who lived in a Brixton council house and claimed income support and child benefit, drove a Mitsubishi Shogun 4x4. Kasonga sported Rolex watches, Oswald Boateng designer suits and even had his name hand-stitched into the label of a £1,400 Saville Row suit and his initials embossed onto the sole of a £1,000 pair of shoes.

After receiving an average of 12 reports per day from victims complaining that cheques were being cashed from chequebooks they had never received, Barnet police mounted Operation Bangor in 2004, uncovering the huge fraud operation.

In April, 45 people were arrested in raids around the country, 23 of whom were found guilty of offences including handling stolen goods, forgery, using a false instrument, converting criminal property and deception.

Twenty of them have already been sentenced, including: Ambrosio Rodrigues Pereira da Gama, 32, of Colindale Avenue, Colindale, who was given 33 months imprisonment for forgery, and was recommended for deportation; Dapinto Silva, 47, of Russell Gardens, Golders Green, who was sentenced to a 180-hour community punishment order for handling stolen goods; and electrician Francisco Luafa Nzinga, 36, of Springwood Crescent, Edgware, who was jailed for three months, and given a suspended sentence of two years and a 150-hour community punishment order for handling stolen goods.

Speaking outside Harrow Crown Court on Tuesday, Detective Inspector Murray Duffin said: "Our investigation began when we were getting 12 reports a day of stolen chequebooks. We got to 220 suspects around the country and stopped counting.

"We then took the top 40 suspects and went after them. Some might not have lived in palaces but they would spend £2,000 on a suit or £500 on a pair of shoes.

"They would have got away with it a lot longer if they hadn't been greedy. That's all it comes down to."

Mayue-Belezika was due to be sentenced yesterday, while Kasonga is due to be sentenced tomorrow.