Siobhain McDonagh, the Labour MP for Mitcham and Morden, will be investigated by a Government watchdog following her £35,000 stationery bill.

Government figures released in October revealed that Ms McDonagh spent more on stationery and postage than any other MP, using £35,207 of pre-paid envelopes and spending another £13,900 on stationery during the last financial year.

She will now be investigated in a Parliamentary probe which will also look at other big spenders, including Liam Byrne and Margaret Hodge.

Ms McDonagh was also the biggest stationery spender in 2003/04 with a bill of £31,845 and came second in 2004/5 with £37,442.

She has held the Mitcham and Morden seat since 1997 and has a 12,560 majority.

At the time, a spokesman for the MP said the stationery had been used to contact constituents about significant local issues.

This included the potential closure of St Helier Hospital and the proposed Eastfields railway station in Mitcham, both of which have had successful outcomes.

"Siobhain sends out lots of letters to her constituents because she wants to be the hardest working MP that she can," he said.

"If she did not contact them, she feels she would not be doing her job properly."