If you've been following the discussions about "Big Society" and the rôle of charities, you may be aware of Parliament's Public Affairs Select Committee investigation on the 
Funding of the Voluntary Sector. The minutes of evidence are rather long, but I was very interested by the asides about the distinction between "campaigning" and "service" charities, with some of the questioners being quite hostile to the idea that charities should try to bring about changes in the law or in the way people behave.
The Chief Executive of Marie Curie Cancer care rebutted the claim as follows:
"It seems to me that it’s a  pretty fundamental principle that free organisations and free  associations can campaign-that’s important.  I think there needs to be a  balance between campaigning and service provision, and often charities  will use their experience of providing services to influence public  policy.  They will say, "Look, we realise that caring for people with  cancer requires a different approach, and we’re going to campaign to  ensure that different approach."  There wouldn’t be a hospice movement  if there hadn’t been both the provision of hospices by the charitable  sector and also arguments on the need for more of them.  It’s a  combination that often takes place.  Different charities will make  different decisions about the balance of that.  I think the best  charities combine the provision of direct services and the use of  knowledge to influence policy.  That’s the important principle I think."   
Fired by his example, I'm cross-posting from a piece I did a few months ago on our i-volunteer page about campaigning and animal charities.
Some animal protection organisations see their primary role  as the direct provision of welfare services (for example rehoming  animals), while others are primarily orientated towards campaigning, or  education. A few combine the two, and this may cause them some problems.
On the one hand they may be accused of diverting funds intended for  animal welfare services into "political" activity (with a small p). Or, on  the other, of failing to tackle basic questions of how we ought to treat  non-human animals in favour of "safe" options which are acceptable to  the general population. 
I think this idea that providing services and campaigning are somehow  natural opposites is false and actively harmful. "Speaking out for  animals" may be all very well, but it isn't likely to do them very much  real good unless it's backed by knowledge (which animal welfare  practitioners are more likely to possess than purely theoretical  campaigners). It may do them actual harm if the campaigns are based on wrong,  outdated or incomplete knowledge.
On the other hand if the practitioner sees recurring problems which  could be solved by education or changes in the law, it makes no sense to  say, proudly: "All our money is spent on direct provision of services."
So far as I'm aware, the RSPCA is unique in providing a free service which the State would 
have to spend money to replace if we collapsed. The PDSA provides services which effectively top up the benefits of very poor people who depend on pets for companionship, but there would be no statutory requirement for any kind of replacement. So long as anti-cruelty laws are on the statutes there would have to be at least a minimal amount of enforcement, even if many cases would simply be disregarded as not a priority. So, in a strange, back-to-front way we're almost the ideal "Big Society" organisation, raising our own funds to provide a better service than the state would do, but at the same time saving public money by funding work the state would have to do if we weren't there. The network of RSPCA branches was doing things locally nearly a century before the 
Big Society Network was thought of. "Mending our communities" may be a little too ambitious, but we are providing local services for low-income families with pets.