Click here to see map of confirmed cases and farms placed under restrictions.
He refused to confirm that the source of the outbreak had been established in Northumberland, but added ""We think we have it on track".
The confirmation of new foot-and-mouth cases at the Heddon-on-the-Wall farm and another farm in Essex brings the total number of definite cases up to five.
As well as separate cases at the abattoir and a farm in the same complex, the disease has been confirmed at farms in nearby Great Warley and most recently at Canewdon, Essex.
The National Farmers' Union said it was "disappointed" that another two cases had been identified.
But Kevin Pearce, chief adviser on beef and sheep for the NFU, said it was "good news" that Maff officers believed they had found
the source of the infection and insisted they had taken all necessary precautions.
A Maff spokesman said: "The disease appears to have been at the farm [in Northumberland] for some time before the Essex case was confirmed.
"We believe that this farm could be the source of the disease."
With the weekend approaching, ramblers and other non-essential visitors have been warned to stay away from rural areas, and hunting and some racing is cancelled.
Exclusion zones
A pig farm in Aberdeenshire is one of a number in Scotland now being tested.
As the disease spreads, animal exclusion zones have also been imposed around farms in Buckinghamshire, the Isle of Wight, and Gloucestershire as well as around the sites of the Essex outbreaks.
The chief of the animal health service at the UN Food and Agriculture Organisation, Yves Cheneau, warned that the type of the disease discovered in Essex had reached pandemic proportions.
Shadow agriculture minister Tim Yeo called for better information and for the quarantine areas to be policed to prevent the disease spreading further.
Compensation call
"This is extremely worrying and typical of Maff's dithering attitude to agricultural crises," Mr Yeo said.
Conservative leader William Hague urged the government to clarify the compensation arrangements for farmers affected by the outbreak.
Foot-and-mouth, a viral disease which causes blisters on the mouth and hooves of livestock, is highly contagious but poses little threat to humans.
UK farmers are already counting the cost of the total ban on exports of British livestock, meat and milk.
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