The main Australian war cemetery in the UK has been targeted by vandals who sawed through a flagpole and spray-painted a memorial on the eve of Anzac Day.

The attack took place at St Mary's churchyard in Harefield in Middlesex, outside London.

More than 100 Anzacs and one Australian nurse, treated at the nearby Harefield Hospital during WWI, are buried on the site.

The Commonwealth War Graves Commission (CWGC), which looks after the graveyard, said today's Anzac Day service would still go ahead, after repairs had taken place.

"Disgusting, absolutely disgusting, for what these lads gave up for us - to be treated like that is just shocking," the commission's Barry Rushton said.

The graves at Harefield have a unique scroll design which was chosen by Anzac patients brought to Harefield - then known as Australian Auxiliary Hospital No. 1 - for treatment from Europe and the Middle East.

Earlier this year the CWGC restored the graves of the Australian servicemen buried at Harefield.

"Ahead of the ceremony, we will either make a clean cut through the pole and have it erected at a lower height, or we will support the pole with brackets," a CWGC spokesman said.

"It will be safe and usable for the ceremony.

"The vandalism is very upsetting for the Commission after all the work that has taken place over the last three months."

Harefield's annual Anzac Day service, which features local school children laying flowers on every grave, started in 1921.

A new visitor information panel featuring smartphone technology revealing the personal stories of some of those buried on the site was also targeted by the vandals.

The CWGC said it was not yet known if the panel unveiling will go ahead.