To me, the people who are in the Tufton St mafia could not be more 'establishment', in background, contempt for the lower classes and lack of any interest in social mobility.
If the 'real' establishment act as a counter balance to these morons, as you suggest, then they would seem to be a more benign force against the extremist element, than I give then credit for.
To me, the establishment (as much as uou can say such an abstract concept exists) is less about maintaining relatively centrist politics and more about ensuring that social mobility is limited to a superficial level that doesn't upset the position of the richest 1%. Whilst making sure that the other 99% is exploited to a ridiculous level.
And that's what Tufton St /etc is all about
Of course, you might think that maintaining centrist politics and ensuring restricted social mobility are the same thing. I wouldn't - well certainly nowhere near compared to the wet dream that the 'establishment' at Tufton St would like to implement.