* FTSE 100 index rises 0.4 percent
* Imperial Tobacco gains on positive outlook
* Housebuilders gain after Persimmon results
By Atul Prakash
LONDON, Aug 19 (Reuters) - Britain's top share index climbed to its highest level in nearly three weeks on Tuesday, tracking strong gains in the U.S. market, with positive corporate news helping companies such as Imperial Tobacco and Persimmon.
Imperial Tobacco advanced 1.6 percent after saying it expected to report modest adjusted earnings growth in the full year after volumes from its top growth brands rose by 3 percent in the first nine months.
UK housebuilders gained after Persimmon posted a 57 percent rise in pretax profit. It sold 6,408 new homes in the six months to end-June and said it was trading ahead of last year in the traditionally slower summer period.
"This is another strong set of results from a housebuilder, backed up by substantial investment in the land bank, very strong free cash flow generation, an improved balance sheet and a significant payout to shareholders under the group's capital return plan," Mark Cartlich, analyst at Sanlam Securities, said.
Persimmon results came in a day after Bovis Homes posted strong first-half results, boosted by a record number of completions, and said it expected to see a significant increase in 2014 profits.
The Thomson Reuters UK Homebuilding index rose 1 percent, helped by a 1 to 3.6 percent rise in shares of Persimmon, Bovis Homes and Barratt Developments.
"The numbers (from housebuilders) are reassuring. Demand and house price inflation have been very strong and that has been getting reflected in the figures that we have been seeing," Henk Potts, director of global research at Barclays, said.
"But there are some constraints from the supply side and we have to see what demand looks like once interest rates start to rise."
The UK blue-chip FTSE 100 index was up 0.4 percent at 6,769.44 points by 0909 GMT after rising to its highest since late July, also helped by fading investor concerns over the Ukrainian crisis.
Ukrainian government forces reported new successes overnight, building on a weekend breakthrough when troops raised the national flag in Luhansk, a city held by pro-Russian separatists since fighting began in April.
However, gains in the broader market were capped by sharp falls recorded by some individual companies.
Global miner BHP Billiton fell 3.6 percent after reporting an 8 percent rise in second-half underlying attributable profit to $5.69 billion, slightly below forecasts.
It also held off announcing a highly anticipated buyback, disappointing investors who had been hoping for a buyback of up to $8 billion, according to UBS estimates. (Editing by Andrew Heavens)