A mum says a neighbour’s “unlawful” home extension has stopped her from being able to keep watch on her daughter playing in her garden.

Kerrie O’Sullivan, who lives in Woodland Way, Mill Hill, said the extension at the back of the property below hers bore “no resemblance” to the original plans – which she had supported.

As well as blocking the view of her garden, she claimed water was pooling on the flat roof – originally supposed to be part-sloping – and leaking into her home, causing cracks and damp.

Barnet Council planning bosses had recommended the extension be given retrospective planning permission, claiming it had “an acceptable impact on the amenity of all neighbouring occupiers”.

But councillors refused permission after hearing evidence at a meeting of Hendon area planning committee on Monday (November 18).

Ms O’Sullivan told the meeting the extension was an “unlawful development in significant breach of what was previously approved”.

She added: “What has been built has no resemblance to the original plans and has been built to an entirely flat roof, higher than originally agreed, which wraps around my entire property.

“The flat roof now sits 250mm below my bedroom windows.

“The excessive height and raised roof light are obstructing my view to my garden. I have a 30ft garden I can no longer see, and if my daughter wishes to play in the garden, I can no longer supervise her from my window. It is not safe for her to play there.”

Owen Dawson, who co-owns the property below with his wife Evelie, expressed regret that there had been a “small deviation from the original application”.

He told the meeting he and his wife had been living in temporary accommodation when building work on the extension started and “were not informed by our contractors or by building control that a deviation of this small size would need further planning approval”.

Mr Dawson claimed it had taken neighbouring residents two years to flag up their concerns – and if they had done so earlier, the issues would have been addressed.

He said: “It is difficult to see how our structure – even with the 0.6m deviation, not 1m – can be credibly said to adversely affect outlook.

“There is no impact on light and, as the report highlights, the elevated position of 49A means a substantial proportion of their garden is, in fact, still visible and [the extension] has little to no impact on this view than had the deviation not occurred.”

But Cllr John Hart (Conservative, Mill Hill), said the development was “far too large compared with the original application”.

He added: “I do not see that the work or, of course, the side effects on the property upstairs, can be really accepted as good design.

“To say that this should be accepted means to say that, broadly speaking, you build what you like…and undermine the planning system we wish to uphold.”

Committee members voted by five votes to two to reject planning officers’ recommendations.

They then voted by the same majority to refuse permission on the grounds that the structure led to a loss of amenity for a neighbouring resident.