From their website (https://www.fosters.co.uk/faqs/, retrieved July 2017, confirmed September 2018)
Q. Is Foster’s suitable for vegans/vegetarians?
A. I’m afraid not.
Company Email (September 2014):
"Fosters [in the UK] is not suitable vegetarians as it is clarified using isinglass finings which are fish derived"
Company email:
"I can confirm Fosters is not suitable for Vegetarians and Vegans."
Also, from the FAQ:
Q. Is Foster's suitable for vegans/vegetarians?
A. I'm afraid not.
Foster's UK
by Foster's UK
Not Vegan
This product is listed as not vegan friendly.
What the company told us
Correspondence on record, with the date of each entry.