A FAKE aristocrat used his alter ego to weave a complex web of lies and deceit for 20 years, a court was told yesterday.

Mr Marc St Leger, 51, was said to have managed to convince the British upper classes that he was the Marquis St Leger, 10th Viscount of Doneraile.

Mr Don Tait, prosecuting, told Bristol Crown Court Mr St Leger set up a bank account with Coutts, the Queen's bankers, even though he had no cash, and even became a member of a committee of Irish peers. But Mr Tait said the defendant lived in a modest house in Swindon with his elderly mother.

He said he had been born Keith Alfred Andrews.

Mr St Leger is accused of obtaining jobs with Wiltshire County Council and the Salvation Army using false CV and application form details and attempting to secure a mortgage by deception. He is also accused of trying the obtain by deception credit balances from the estate of the late Ethel St Leger.

He is further accused of falsely claiming #16,970 of Invalid Care Allowance from the Benefits Agency and #2435 of income support, both using his original name, Keith Alfred Andrews.

Mr St Leger, of Kennedy Drive, Swindon, denies three counts of obtaining pecuniary advantage by deception, two counts of obtaining property by deception, one count of attempting to obtain a pecuniary advantage by deception, and one count of attempting to obtain services by deception.

Mr Tait said the defendant began leading a double life about 1975, calling himself Marc Philip Justin Onslow Berkeley St Leger Curzon. He invented a whole new family tree for the real St Leger family, which can trace its history back to the Norman conquest, taking advantage of a dispute in the line of succession.

He claimed his mother was Joy Chantal Helene de Burgoyne of Paris and Tours and that he had been married to Marie-Louise, daughter of the Duc de Brissac of Paris. Mr Tait said he claimed to have two sons but later told police his wife and children died in a car crash in Australia in 1975.

''Twenty years ago not only did this man adopt a different name he also adopted a completely different personality and alter ego,'' the prosecutor said. ''Since that time these two personae have been running in tandem.''

Mr Tait alleged the alter ego was used to fool people and ''also allowed him to mix with some members of the aristocracy, some of whom were fooled''.

The hearing continues.