The Royal Parks has been forced to spend more on battling tree disease at a time when the service has to find year-on-year cuts.
It spent £179,000 on the problem this year but it would have much more without the benefit of thousands of hours of volunteer work. In Richmond Park alone the incidence of oak processionary moth (OPM) has rocketed from four nests in 2009 to 4,188 this year.
OPM has become established in south-west London and has infected Bushy and Richmond Parks, both in the London Borough of Richmond, but the other Royal Parks are not yet affected.
Chief executive Linda Lennon said she and her team are very concerned about the issue. Richmond Park is a site of special scientific interest so nests on 99 per cent of the trees cannot be sprayed. Instead volunteers have spent 1,026 hours identifying the nests and then Royal Parks operatives must go into the trees to remove them manually.
"We're diverting income that we're generating into tree diseases in a way that we wouldn't have done several years ago. We have a stark choice - can we raise additional income to deal with that or do we cut elsewhere? I don't think we have any choice but to put money into our trees. We have 250 species and we're reviewing how much it has cost us."
Lennon called for increased import controls, adding that the Forestry Commission should have the right to be able to act quickly on diseases. "Massaria is one that's really concerning us this year. We've spent more than £80,813 on branch removal and we've had 1,400 man hours of surveys and spent £30,000 on soil improvement. Drought is a key issue."
Speaking at the opening of a new walkway and bridge at Richmond Park, local Conservative MP Zac Goldsmith said we should "make use of our island status" and charge a levy on imported plants.
He criticised the Government for not acting sooner on OPM. "They knew it was a problem and it now costs four or five times more than it should have. The law should be changed.
Victoria Tower Gardens - Building proposed
The House of Commons Commission has submitted a planning application to Westminster Council to build an education centre in Victoria Tower Gardens.
The public park, situated next to the Palace of Westminster, is run by the Royal Parks. Chief executive Linda Lennon said the one-storey structure would not be permanent.
"It represents a loss of 2.5 per cent of the green space," she added. "My team is working very closely with them on the design and on how you can best increase biodiversity in the area. The design has changed quite significantly as a result of that."
The plan includes a green roof and landscaping. Landscape architect Kim Wilkie worked on the project.