Poo in book dumped outside Abbott's office

NSW Police are investigating after faeces hidden inside a book was left outside Tony Abbott's Sydney electorate office.

Faeces placed inside a hollowed out book has been left outside Tony Abbott's electorate office. (AAP)

A poo hidden inside a hollowed out book has been dumped outside Tony Abbott's electorate office in northern Sydney.

The faeces was placed inside the book with the word "Unpopular" written on the cover, according to photos published by News Corp Australia.

Police are now investigating the item found outside Mr Abbott's Manly office on Tuesday morning.

"Police attended and the item has been collected," a police spokesman told AAP.

The former prime minister's office has been contacted for comment.

Police also appealed for information late last week after posters featuring Mr Abbott appeared in his Warringah electorate with expletives written across his forehead.

Other posters had "Pell" written across them - an apparent reference to the Liberal MP's friend and convicted pedophile Cardinal George Pell.

Mr Abbott on Tuesday released a video on Twitter featuring former prime minister John Howard backing his campaign.

Mr Howard said Warringah contained many people who were "not wealthy" but "successful through hard work and enterprise".

"Many of them have arranged their retirements on the basis of existing laws," the 79-year-old said.

"(Bill) Shorten wants to hit them with new and unfair taxes and there's only one candidate, Tony Abbott, who'll fight tooth and nail to prevent this huge tax impost."

Mr Abbott is facing a serious challenge from independent Zali Steggall, with recent opinion polls suggesting he'll struggle to retain the seat he's held for 25 years.