Following my earlier post about Plymouth I have had a look at the detailed results in Dudley. This is a council where Labour have made 13 gains and thus decisively taken power from the Conservatives. But in 11 of the seats they gained their majority was smaller than the UKIP vote. Frequently it was much smaller.
UKIP have increasingly repositioned themselves as a Conservative Party. Some of their voters in Dudley would have abstained if there hadn't been a UKIP candidate, a few might have voted labour. But it is reasonable to deduce from these figures that UKIP's intervention didn't just help Labour gain Dudley but that it was a critical help.
In Thurrock it is also quite likely that Labour would not have been able to make it without UKIP. Labour needed 25 seats for an overal majority and won 26. They included Stanford-le-Hope West where they had a majority over the Conservatives of 30 and the UKIP candidate polled 182. In Stanford East and Corringham the Labour majority was also much smaller than the UKIP vote.