UEFA will allow host cities to upscale plans for supporters to attend Euro 2020 matches should conditions around the coronavirus pandemic improve.
The European governing body asked for the 12 host cities, including Glasgow, Dublin and London, for their proposals on how many fans they expect to be able to accommodate today.
The British government has announced plans for a number of test events, including a 21,000 crowd for the FA Cup final on May 15, with a view to having Wembley full for at least some European Championship games.
Wembley will see England open their Group D campaign against Croatia on June 13, before then welcoming Scotland on June 18 followed by the Czech Republic.