"Costa has always been the nation's favourite coffee shop and now it's the taxman's," said Andy Harrison, the chief executive, reports the Daily Telegraph.
Starbucks is struggling to overcome the damage to its reputation from the tax row. It paid just £8.5M in corporation tax in 14 years on UK sales of £3Bn, and a pledge last week to voluntarily pay £20M to the taxman to defuse the row appeared to backfire triggering protests at branches across the country at the weekend.
While Harrison acknowledged his rival had "issues", the company pointed out that Costa has been performing well right through the recent recession as UK customers have refused to give up their caffeine fix as they cut back to cope to with austerity.
Like-for-like sales at Costa, sales at those coffee outlet open for a year or more, grew 6.9% in Great Britain in the 13 weeks to 29 November and 7.1% overall, the company said in a trading update.
Costa's strong performance helped the group deliver like-for-like sales growth of 3.3%, as growth at its hotels and restaurants slowed since the first half when sales were lifted by wet weather and the Olympic Games.
Sales at Premier Inns hotels were 2.5% like-for-like, down from 3.8% in the first half. While at its Beefeater and Brewers Fayre restaurant chains it fell from 3.4% in the first six months to 1.9% with the growth driven by a higher spend per head.
Harrison said Whitbread was on track to deliver full-year results in line with expectations in a challenging "economic environment".
Whitbread is expected to report full-year pre-tax profit of around £348M, up from £320M last year.