The expenses scandal began because the mole who caused the leak was angry about inadequate equipment for the armed forces, the Daily Telegraph said.
The newspaper says staff who worked in secrecy processing the MPs' receipts were guarded by moonlighting servicemen on leave between tours.
They became angry when they learned of MPs' lavish claims when soldiers had inadequate equipment, the paper says.
Many servicemen were working so they could buy better kit, the paper adds.
http://news.bbc.co.uk/1/hi/uk_politics/8274041.stm