IT APPEARS that it is not just Peter Slipper who is spending up big in the office of the member for Fisher.

An investigation into the spending habits of the Speaker's electorate staff has revealed that an unnamed employee spent more than $34,000 in travel expenses in a year - more than 10 times that of any other staff member. The services claimed for include airfares, travel allowances, and taxis.

Documents obtained by The Sun-Herald under freedom-of-information laws show that the other six employees had travel expenses ranging from $427 to about $3000 each.

The documents detailing electorate staff travel for the 2008-09 financial year also caught the attention of the Department of Finance because its allocation was overspent.

The travel budget was $45,772 but total payments were $52,951.13, over budget by $7229.13.

Internal emails from the entitlements management branch of the Department of Finance show Mr Slipper was warned three times that his travel budget was approaching the limit but it continued into the red.

When Mr Slipper was pulled up, he asked that travel allowance paid to his wife, Inge-Jane Hall - who works in his office as an electorate officer - be reallocated to the family travel budget, reducing the amount that had to be repaid.

Mr Slipper declined to comment to The Sun-Herald about his staff travel budget.

The revelations about staff spending come as the Australian Federal Police continue their 18-month investigation into unrelated allegations against Tim Knapp, a long-time adviser to Mr Slipper.

The federal police last week yesterday confirmed to The Australian Financial Review that they had begun an investigation, codenamed Operation Radbyrn, into Mr Knapp on October 5, 2010, after the Department of Finance referred the matter in June of that year.

It has been reported that Mr Knapp, who is said to have worked for Mr Slipper for at least 10 years, is being questioned over two matters. One involves the alleged use of a Commonwealth fuel card that was in Mr Slipper's name and used in a private vehicle.

The police are also investigating claims that Mr Knapp may have taken leave from Mr Slipper's office even after he had been paid out for the entitlements.