The website is www.portalrestaurant.com or www.portalrestaurant.co.uk.
"A modern European restaurant with strong Portuguese, French and Mediterranean influences[...]" says its website.
From the website I also got its location in London:
> Five minutes walking from Barbican and Farringdon tube stations (Circle/Yellow line).
> Six minutes walking from St Paul’s Cathedral.
A curious issue here is that, in the best of my knowledge, this is the very first restaurant in London named after a Port Wine brand, Quinta do Portal.
Even all the Portal Restaurant's merchandising is the same as Quinta do Portal's Ports.

The restaurant opened in London on June 22, 2005.
I've never been there myself


Address:
Portal Restaurant
88 St John Street
London EC1M 4EH
Telephone +44 (0)20 7253 6950
Web: http://www.portalrestaurant.com
Open for lunch and dinner
Monday to Saturday 12.00 to 15.00 then 18.00 to 22.15
Bar drinks and Petiscos 12.00 to 22.15