A former senior manager at a Commonwealth agency has admitted he defrauded the Tax Office of almost $380,000 over several years by lodging false documents on behalf of two fake aviation businesses.

Andrew Charles Richards, 39, pleaded guilty to two counts of obtaining a financial advantage by deception, and two counts of using forged documents, when he appeared the ACT Magistrates Court on Wednesday.

He was originally charged over 53 offences, including three fresh charges that were laid in court this week, but the prosecution rolled all the matters into four charges.

Richards registered for GST as a sole trader under the business name Infinite Aviation, which he said provided flight training, chartered aircraft and exported custom aircraft parts, in 2006.

He claimed $227,256 through 44 business activity statements he lodged on behalf of the company between 2007 and 2010, facts tendered in court showed.

Richards also avoided paying $13,872 in GST that he should have paid for goods he imported into Australia.

Court documents showed Richards had also registered another company, the National Register of Encumbered Aircraft, with himself as sole director, in 2008.

He lodged eight business activity statements and claimed $151,337 for the period between 2008 and 2010.

But court documents said Richards was employed as a senior manager at Airservices Australia during that time and neither of the business entities in his name were genuine.

Some of the amounts of money he claimed in business statements he filed were false and Richards also provided a series of fake documents to the ATO to support his claims.

The fraud was discovered during an audit of the two enterprises in September 2010.

The Tax Office received a letter from Richards a month later in which he deemed himself “unsuitable to operate any kind of business in the future” and said he would pay back any money he owed and any fines.

In an interview with auditors he made further admissions and said he should not have done what he did.

Richards was also charged for providing a forged birth certificate, changed to show the birthdate he had included in paperwork for his business ventures, when he started work with Airservices Australia.

The matter was committed to the ACT Supreme Court for sentence. It will appear in March for mention