EU elections results represent proportionally so vote for who you least dislike please ... to >at-least counter the UKIP votes.
Unfortunately that's not entirely true. The EU elections in mainland UK use the D'Hondt method which penalises smaller parties, so it can still be advantageous to vote tactically. (In NI they get STV, which is much better). Still, in London, Green party have a current MEP and Lib Dems have previously and were very close in 2014, so either of those are good for getting clear pro-EU votes in (assuming the appearance of TIG/ChUK doesn't split the remain vote too much).
Unfortunately that's not entirely true. The EU elections in mainland UK use the D'Hondt method which penalises smaller parties, so it can still be advantageous to vote tactically. (In NI they get STV, which is much better). Still, in London, Green party have a current MEP and Lib Dems have previously and were very close in 2014, so either of those are good for getting clear pro-EU votes in (assuming the appearance of TIG/ChUK doesn't split the remain vote too much).