The commander of British forces in Afghanistan between 2003 and 2004, Colonel Richard Kemp, said 200 was an important milestone that could sow seeds of doubt in the minds of the British public.
"It's a very significant milestone, it's very tragic, that we should have lost this number of soldiers in Afghanistan.
"The thing it changes, really, is the way people in this country look at what's going on and I think there will be questions asked about whether what we're achieving in Afghanistan and what we're hoping to do in Afghanistan is worth this number of British soldiers lives."
Mr Kemp made clear that he believed this level of sacrifice, although tragic, was the cost of doing a valuable job in defending the UK from a terrorist attack.
And members of the armed forces would not be wavering in the face of a rising death toll.
''The soldiers deployed in Afghanistan will get on with the job. They will be deeply saddened, whether they know the soldiers killed or not, they will be deeply saddened and shocked by every single death, but they are stoic people and will get on with the job.
'Significant milestone' in Afghanistan
"If anything, their resolve to achieve their mission will be increased and refreshed by each and every single casualty they take, because they will want to give meaning to that soldier's life and to his death and they will do that by increasing their own determination to achieve their objectives."
It was difficult to estimate enemy losses, said Mr Kemp, but the Taliban had suffered much heavier casualties and had changed their tactics as a consequence, focusing on roadside bombs rather than combat.
BBC world affairs editor John Simpson, in Kabul, said there had been some British success closing the Taliban down in the south, paving the way for the election in a week's time, but concerns persisted.
"There must be questions about why British troops have suffered relatively speaking more than American troops.
"Are their tactics better or do they have gadgets that we don't have? Those kind of questions are very important."
It was also clear, he said, that the British had found no answer to the Taliban's use of roadside bombs.
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