Aug 1 (Reuters) - British scientific instruments maker

Spectris ( SEPJF ) has agreed to private equity firm Advent's

sweetened takeover offer worth 4.8 billion pounds ($6.38

billion), including debt, as the battle for Britain's biggest

takeover target of the year heats up.

Shares in the London-headquartered company closed up 2.2% at

4,078 pence, a near four-year high. They have more than doubled

in value since Advent made its first buyout proposal on June 9.

Advent is now offering Spectris ( SEPJF ) shareholders 40.72 pounds

per share in cash and an interim dividend of 28 pence, topping a

4.7 billion pound offer from U.S. investment firm KKR,

which also included debt.

KKR is evaluating its next steps and will update the market

when appropriate, it said in a statement after Spectris' ( SEPJF ) board

withdrew support for its offer.

The U.S. firm also recently lost out on British healthcare

real estate investor Assura, which recommended a rival

bid from Primary Health Properties ( PHPRF ).

Britain's subdued valuations and relative stability have

attracted overseas buyers, with a flurry of bids in recent

months highlighting the appetite for UK assets.

Spectris ( SEPJF ) provides hardware and software to sectors including

pharmaceuticals, steel and automotive.

($1 = 0.7528 pounds)