underfish - I suspect that it may well be possible to arrange a flight in and out of the UK on Easyjet with your visa situation. However, when you arrive at Barcelona airport for a flight via London to Tallinn, you are likely to need ample paperwork to show checkin / gate staff (who are unlikely to be familiar with TWOV rules and will just see you as a Russian without a UK visa) to reassure them that they won't get into trouble for letting you on the plane because of potential visa issues.