"Many authorities do not currently have funding or sufficient staff to track the occurrence of the pest," he told Horticulture Week.
"It is becoming increasingly clear that ideas of eradicating the pest or geographically holding the line are becoming unrealistic, and in the long term we are going to have to live with and manage the presence of OPM to its natural range in the UK."
He added: "Whilst natural control via parasites may be developing and research may help us in many ways, it looks inevitable at present that the problem will become far more widespread - despite the best efforts of many organisations and individuals including many LTOA London member authorities."
A map (above) published in September 2018 by the Forestry Commission, which is co-ordinating the response to the pest, shows it to be present in nearly all London boroughs, as well as in several authorities outside of London for the first time.
"As the perimeter of the outbreak recedes concentrically from London, the area affected grows at a greater rate," Lofthouse noted.
Arboricultural manager for a south London borough, Dave Lofthouse is a former LTOA chair and member of its OPM working party. He co-authored its 2015 OPM position statement, which questioned at the time whether the policy of control and containment outside the Core Zone, shown in red on the above map, was "realistic".