lat = float(request.GET.get('lat'))
lng = float(request.GET.get('lng'))
a = Authority.objects.get(area__contains=Point(lng, lat))
if a:
    json = simplejson.dumps({'name': a.name, 'area': '{replaceme}', 'id': a.id}
        ),
return HttpResponse(json.replace('"{replaceme}"', a.area.geojson), mimetype
    ='application/json')
Using Python simplejson to return pregenerated json