The Food & Environment Research Agency (FERA) said outbreaks on a Durham planting site and a West Yorkshire nursery were confirmed in the past two weeks with most of the others on new sites during late August.
FERA inspector Derek McCann said: "There is still no evidence to suggest that it has spread into the natural environment in the UK, so we still have a chance to eradicate it before it does.
"The responsible actions of the nurseries and site owners involved in the current findings have meant that we have been able to follow these up quickly, giving ourselves the best chance of preventing the disease spreading."
The HTA has called for a moratorium on ash imports, which FERA and the Forestry Commission have welcomed ahead of a consultation on a pest risk analysis drafted by tree health scientists at the Forestry Commission's Forest Research Agency. It is inviting views by 26 October.
McCann added that he could not rule out other infected consignments having been received.
The planting sites are a Forestry Commission woodland at Knockmountain near Glasgow, a car park in Leicester, a college campus in South Yorkshire and a property in County Durham.
The nurseries are in Buckinghamshire, North Yorkshire, Surrey, West Yorkshire, Cambridgeshire and Lincolnshire. For further details, see www.fera.defra.gov.uk/plants/consultations/index.cfm.