It's Still Preliminary Data.

However even the BBC is acknowledging that they've demonstrated causality.

It's not a coincidence. The Oxford vaccine is causing these blood clots. 

http://www.xinhuanet.com/english/europe/2021-03/31/c_139847842.htm

If those findings are confirmed then the WHO is going to have to change its guidance.

That it should only be used as a last resort. Where no other vaccine options are available.