There is little, it would appear, that can be done to stop the alley gating from going ahead - as I wrote originally, this is private land so the residents are quite within their rights to prevent public access.
Full credit, though, to Merton Council for giving a full and detailed response, with bonus points for including the phrase 'lewd and libidinous'. I think if I was going to be lewd and libidinous I would find a better location than a Garth Road alleyway, but I digress.
Herewith Merton Council's response:
"The land being used as a public footpath, is private land owned by the residents who back onto it and was never intended for public use.
Numerous accounts of anti social behaviour have taken place in this private alleyway for a number of years. This is extremely distressing for the residents who live here and witness the events.
The problems consist of dog fouling left behind by dog owners, trespassers loitering, drinking, littering, taking drugs, using the alley [as] a public toilet and lewd and libidinous acts.
On 4 January 2005 a member of the public had an accident at the steps on Sutton’s border, while using this private alleyway as a shortcut to Garth Road, Morden. This person is in the process of making a claim against one of the involved Garth Road property owners. This claim and the above mentioned anti social behaviour, has lead the landowners to take steps to secure their land.
The London Borough of Merton has introduced the Alleygate Scheme to help its residents secure their property. Residents who decide to gate their privately owned alleyways, can do so without permission from the council.
However, if they wish to receive grant fund from the London Borough of Merton, they must follow the strict guidelines, laid out in the London Borough of Merton “Guide to Alleygating” booklet. You can find this booklet at the following website address: www.merton.gov.uk/alley-gating
The decision to gate and fence this area was taken by the involved Garth Road residents. The public notice was placed in the alleyway and in the Merton Guardian by the London Borough of Merton Alleygate Co-ordinator on Thursday 18 December 2008 because the Lynton Alleygate Scheme Committee have applied for grant funding towards the cost of the gate and fencing.
The Lower Morden Safer Neighbourhoods Team have had some involvement in this alleygate scheme and have spoken to some of the residents about the incidents of anti social behaviour.
A map [of the area] obtained via the London Borough of Sutton Website shows any Public Right of Way in red and the Sutton Borough boundary in dark blue. The map shows that there is no Public Right of Way through the alleyway in question.
The Public Right of Way signpost at the top of the steps at the Sutton border, is pointing to and relates to the path that is to the left of the alley, if you are approaching the area from the Trafalgar Avenue end.
[To view the map click here and search for 37 Trafalgar Avenue]. Click on the Service window in the top right hand corner of the screen and scroll down to Public Right of Way. This will highlight any Public Right of Way in red.
Whilst I understand the inconvenience that securing this private alleyway will cause to Sutton residents and persons who park their vehicles in Trafalgar Avenue, Worcester Park, to access their place of work in Garth Road, Morden it is without setting precedence [sic] that the London Borough of Merton is considering releasing funds towards the Lynton Alleygate Scheme.
The involved residents have met the criteria needed in order to apply for a grant towards their Alleygate Scheme and their application must be considered.
The land in question is privately owned and the property owners are well within their rights to gate and fence their alleyway. The alleyway is not owned, or maintained by the London Borough of Merton. Therefore the residents of 101 – 115 Garth Road can secure their land without any authorisation or funding from the London Borough of Merton."