* FTSE 100 ends down 0.5 percent
* Admiral falls as Brexit vote affects solvency ratio
* Indivior climbs after clinical trial result
* Laird boss to join Cobham, shares diverge (Updates prices at close, adds detail)
By Kit Rees and Alistair Smout
LONDON, Aug 17 (Reuters) - A slump in Admiral shares dragged Britain's top stock index down further from the14-month highs it hit on Wednesday, after the car insurer saidthat market volatility caused by Britain's vote to leave the EUhad hit its solvency ratio.
Shares in Admiral, which missed analyst estimates with itsresults, fell 7.7 percent, their biggest fall since November2011. Admiral also warned of the additional fallout from Brexitof economic uncertainty and interest rate and forex volatility.
"Although the pre-tax profit of 189.5m pounds was in linewith our forecast, it represented a small miss againstconsensus, itself a rare occurrence for Admiral," Shore Capitalanalysts said in a note.
"However, it was the 'noise' around the group's Solvency IIposition, which dropped sharply in H1 16, and Brexit which werethe most worrying, to us, and does question the wisdom ofAdmiral's return-of-capital strategy."
The stock was the stand-out loser on Britain's FTSE 100, which was down 34.77 points, or 0.5 percent, at6,859.15 by the close, extending Tuesday losses.
The mid-cap FTSE 250 was down just 0.3 percent.
Bucking the trend, Indivior surged 8.8 percent to close atan all-time high after its drug for opioid use disorder passedits latest clinical trials.
Infrastructure firm Balfour Beatty rose 3 percentafter beating first-half expectations and resuming dividendpayouts. It said there was little sign yet of the Brexit voteaffecting its markets, but that it was too soon to know how thedecision would eventually play out.
"The big news from Balfour Beatty this morning is thereinstatement in the dividend," Edison Investment Researchanalyst Stephen Rawlinson said.
"With the order book up 11 percent at 12.4 billion pounds,the legacy contracts well understood and in many cases resolvedand with both risk and cash management under tight control, itis perhaps appropriate that the shareholders get the benefit ofthe improvement earlier than many expected."
Fellow construction firm CRH rose 0.9 percent andwas among the top gainers on the FTSE 100.
The biggest mid-cap faller was tech firm Laird, down6.9 percent, after Cobham announced that Laird's bosswould replace the Cobham CEO by the end of the year.
Defence company Cobham's shares advanced 0.4 percent. (Editing by Louise Ireland)
