Europe open: Stocks slip lower ahead of ECB

Markets slipped at the start of the session after the White House's tax cut proposals released overnight underwhelmed analysts, with investors also playing it safe ahead of the European Central Bank's policy meeting later in the day.

As of 08:39 GMT the benchmark Stoxx 600 was down by 0.39% to 387.23, with Germany's Dax off by 0.26% to 12,439.96 and the Cac-40 losing 0.26% to 5,274.80.

"A negative opening call comes after US bourses closed lower, disappointed with an underwhelming Trump tax announcement, and Asian stocks had a lacklustre session overnight as a consequence. Nice ideas, but far from a done deal, merely adding to investor frustration about the lack of progress on all those election pledges that helped fuel risk appetite and markets to recent highs," said Mike Van Dulken, Head of Research at Accendo Markets.

Overnight, the White House's top economic adviser, Gary Cohn, unveiled the broad contours of the US administration's plans to reduce taxes and streamline the tax code.

Michael Levy at Berenberg Capital Markets said the tax reductions Trump was aiming for were "way too aggressive".

Nevertheless, Levy does expect a package of tax reform to be passed this year and believes it will inevitably include a degree of fiscal stimulus for the economy.

Against that backdrop, the key event on Thursday is the European Central Bank's policy announcement at 12:45 GMT, followed by chief Mario Draghi's press conference at 13:30 GMT.

Investors are watching for any hint that the Governing Council might tweak its message following the results of the first round of voting in the French elections, which have led to a reduction in the perceived risk that the single currency block might break-up.

The above will coincide with the release of data on US durable goods orders and foreign trade in goods for March, alongside weekly initial unemployment claims data all at 13:30 GMT.

GfK's consumer confidence gauge for Germany shot higher from a reading of 9.8 points in April to 10.2 for May.

A preliminary estimate for German CPI in April is scheduled for release at 13:00 GMT.

Spain's harmonised CPI unexpectedly rose at a 2.6% year-on-year clip in April, up from 2.3% in the month before.

German chemicals-maker BASF reported better than expected operating profits, telling shareholders it now believes the top end of its 2017 forecast range for profits, for a rise of up to 10%, is now within reach.

Shares in Deutsche Bank are lower despite the lender having more than doubled its first quarter net profits to €575m.

Airbus reaffirmed its financial targets for the year despite a 52% slump in first quarter profits.