Unfortunatly you cannot say no. Well you can of course but you will loose the support you receive. The Section 4 or 95 application states accomodation is on a no choice basis, and you apply on this basis. You can appeal and ask them to look again, provide eveidence such as letters from your churchand firends to say they support you in London. However, in my experiance ( I provide advice and support to asylum seekers and refugees) this is only granted because of either having a child living in a particular area or having a health condition which ties you to a specific area...such as a specialist consultant for example. You can apply for NASS support as many times as you like and there may be a small possibility that you are housed in the area you like just by chance. Hope this helps