Firstly, remember our definitions:
Pluralists, elitists
Insiders, outsiders
Sectional/interest groups, cause/promotional groups
People often struggle with naming insider groups - let's have a think:
The National Farmer's Union is a great example of a core insider - because they are needed on a range of government policy AND have expertise.
The National Trust is a great example of a specialist insider, as they have such a large membership and are in the public eye.
The WWF, who have expertise on wildlife and nature and work all around the world.
The CBI are are a useful examples because their insider status is under threat! Having previously lost some status due to disagreements with government (eg over Brexit). They had a huge degree of sway, but now are being side-lined after a recent sexual assault scandal.
BUT have been replaced by other groups, such as the Institute for Economic Affairs, a free market think tank. If insider groups like the CBI aren't aligned with the government's views and interests then it stands to reason that they might choose someone more in touch with their views.
The British Bankers Association are certainly well aligned with more free-market, Conservative governments.
The TUC (Trade Union Congress) may have less influence under a Conservative than Labour government, but still may be needed to provide advice to the government on workers' issues, or for negotiations with unions.
A group like the Board of Deputies of British Jews may be consulted on issues to do with anti-semitism, or specifically to issues that affect Jewish people in the UK.
Stonewall are a group who slowly gained insider status, but recent controversies over issues like trans-prisoners and trans rights in general has led to some government organisations distancing them from the group.
It is worth remembering that we have core insiders (eg NFU), specialist insiders (eg the British Meat and Poultry Association), peripheral insiders (who are only rarely consulted by the government, like SANDS), and prisoner groups (who are basically under government control, like Historic England).
There are so many outsider groups, and you know loads of them!
Stop the War, Fathers 4 Justice, UK Uncut, Extinction Rebellion, Fareshare (but are they insiders now?), Animal Liberation Front, Amnesty, Liberty, Prison Reform Trust, Plane Stupid, Gurkha Justice Campaign. And many more!
Remember that these can also be subdivided:
Potential insiders (like the Gurkha campaign or Fareshare), outsiders by necessity (who must be outsiders due to being outside the mainstream like CND or Plane Stupid), and outsiders by choice (who don't want to be associated with government, like Liberty or Amnesty).