Who are the ERG? And why do they matter so much to Brexit?

Since the EU referendum three years ago, an obscure sounding group of Conservative MPs has shot to prominence.

The European Research Group used to provide worthy briefings on European issues. Now it has morphed into a body that exerts huge influence as Parliament debates Brexit – and if and when Theresa May resigns, it’s role in picking her successor as Tory leader and Prime Minister could also be enormous.