If I only have access to single cream can I use this instead of double cream?
The ability to substitute single cream for double (heavy/whipping) cream in a recipe really very much depends on the recipe itself. Unfortunately if it is a recipe that requires the cream to be whipped then usually it is not possible as single cream does not have a high enough fat content to whip - it will not hold any air but will eventually turn into butter if you keep whipping it.
If the cream can remain in liquid form for the recipe then it should be fine to use single cream, though sometimes with precautions. If you are making a custard or something like Nigella's Budino Di Cioccolato (chocolate puddings) from Nigella Express or a panna cotta then single cream can be substituted. If you are adding single cream to a sauce then you need to make sure that the sauce is not too hot as sometimes the cream can curdle or split slightly. This is a particular risk if the sauce contains an acidic ingredient (such as tomatoes). Once you have added the cream then we would also suggest that you avoid boiling the sauce.