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A British butterfly species that was facing extinction thanks to the invasion of a parasitic fly species has undergone a 'dramatic comeback', according to a survey.

Numbers of small tortoiseshell butterflies have increased 22 per cent in the last year to 63,238 according to the Big Butterfly Count.

The species had been in danger of disappearing from this country after it lost three quarters of its numbers since the 1970s. 

The small tortoiseshell butterfly has seen numbers grow by 22 per cent this year, following on from a 388 per cent boom in population last year, in what scientists are calling a 'remarkable comeback'

For the first time since the survey started in 2010, the peacock butterfly was the most abundant, with 95,551 spotted between July and August

Loss on habitat, along with the emergence in Britain of a new kind of parasitic fly, are largely blamed for the losses.

Fly species sturmia bella lays its eggs on nettle leaves which are then eaten by unsuspecting caterpillars. The eggs then hatch inside the caterpillar before burrowing their way out.

Scientists say this year's boom in small tortoiseshell butterflies is surprising given that this August was the coldest for 20 years, and also comes after a major increase in numbers last year.

The wildlife charity's conservation surveys manager Richard Fox said: 'After a good summer in 2013, the big question this year was whether butterflies would continue to recover and build up even greater numbers or slip back again.

'Thanks to another amazing turnout from the public, we know the answer is a real mixture.'

And he said its success this year was a combination of factors. 'It had a really good year last year, relatively in the recent history of this species, and it has been able to use that as a springboard to kick on and improve this year.

The common blue saw the greatest increase in population with volunteers reporting 17,819 across the UK, a 55 per cent increase compared with 2013 

However most species in the survey saw their populations decline after the coldest August in 20 years, including the large white (left) and small white (right) species which were badly affected

Ringlet butteflies were among the species who suffered this year thanks to a cold Autumn, with numbers falling 58 per cent to 13,757

'We've had mild weather and lots of warm temperatures but no drought.'

However, the continued recovery for the small tortoiseshell came amid a bad year for the majority of other butterfly species.

In total, 15 out of the 21 species included in the count saw numbers fall compared with 2013 while just six species saw modest increases in population.

Britain's white butterfly species, including the large white, small white and marbled white, did particularly badly this year, as did the ringlet and six-spot burnet.

The common blue saw numbers grow the most, with 17,819 spotted by volunteers between July and August, an increase of 55 per cent, with numbers of red admiral butterflies also rising 43 per cent.

The peacock butterfly was the most abundant species for the first time since the count began in 2010, with 95,551 seen, despite numbers being 30 per cent down on last year. 

The red admiral butterfly, which is spotted across the UK, ddi well this year, with volunteers spotting 25,606 of them, a 43 per cent increase compared with summer 2013

The speckled wood (left) had another good year with numbers up 28 per cent after last year's increase of 31 per cent, while number of meadow brown butterflies (right) fell by 38 per cent

The summer of 2013 was a bumper year for butterflies, with the peacock species booming 3,500 per cent, followed by small tortoiseshells on 388 per cent and brimstones on 380 per cent.

The majority of butterfly species spotted saw triple-figure increases in their numbers, while only six of the 21 most common saw their numbers drop.

This year the mild weather, even during last winter, and lack of drought was good for stinging nettles which the tortoiseshell larvae feed on.

While the cold August could have curtailed adult reproduction, he said, all the species that were covered by the Big Butterfly Count were on the wing for more than just that month.

Many had several generations through the summer while those with a single generation had a long flight period, he said.

Nearly 45,000 people took part in this year's Big Butterfly Count, which is organised by Butterfly Conservation in partnership with Marks & Spencer.