Oil prices wobbled but remained on course for their fifth weekly decline, dogged by concerns over a stubborn supply glut.

European stock markets are "on the back foot, with a host of eurozone PMI surveys... providing a somewhat cautious assessment," said analyst Joshua Mahony at trading firm IG.

Shares in London saw a fourth straight day of losses a year to the day after Britain shocked its neighbours by voting to leave the European Union, with the FTSE 100 index of leading shares losing 0.2 percent.

Sterling strengthened 0.4 percent Friday but Tuesday's close of $1.2661, but this represents a drop of 15 percent from its value the day before the Brexit vote.

"Stock markets have fallen yet again as the disinflation fear is still doing the rounds," said David Madden, analyst with CMC Markets, who added traders were concerned oil's price weakness would put "downward pressure" on inflation, damping down growth expectations.

On Brexit, Madden noted that since this time last year "it has certainly been a rocky ride to say the least."

Eurozone private sector business activity slowed sharply in June but over the second quarter recorded its fastest expansion in six years, a closely watched survey showed on Friday.

Analysts said that while the downturn in the headline readings was disappointing, the economy continued to put in a strong performance.

Data monitoring company IHS Markit said its June Composite Purchasing Managers Index (PMI) came in at 55.7 points, the lowest reading in five months and down from 56.8 in May.