The WCC Labour Group blame WCC for the break up(see below) and RBK&C blame H&F!
The truth will never be known.
The only substantive fact is that it was a bloody silly idea in the first place.
Myers and Pooter got their K's on the back of it: they should be stripped of them.
"Westminster Council’s long-term mismanagement of back-office systems for Hammersmith & Fulham, Kensington & Chelsea and Westminster were at the root of the break-up of tri-borough arrangements.
Councillors in Hammersmith & Fulham had little alternative but to look for other arrangements following grotesque failings in some of the back office tri-borough workings, for which Westminster was the lead borough. From the start of tri-borough, Westminster took charge of an attempt to run all three councils' routine billing and staff hours, pay and pensions administration through one contract.
Westminster Council gave the contract to BT in January 2013 telling everyone that it would save £30m and other councils would be asking to join in. At that point Westminster expected the contract to commence across the three boroughs in November 2013 (for HR) and March 2014 (for finance) and go live soon after.
It didn't. The contract actually went live in April 2015. The reason for the delay, and what happened after the contract did go live, are unfortunately covered by strict rules about commercial confidentiality. It is however in the public domain that Westminster Council's Audit and Performance committee held eight extraordinary meetings over this one contract (all in private sessions)."