England fans with tickets for their final Six Nations match were on Monday warned off selling them on the secondary market.
With Cheltenham Festival also taking place this week, Irish sports fans are expected to travel to the UK in their thousands.
And now holders of tickets for the Saturday’s showdown are asking for up to £4,400 per seat on the secondary market on Monday, which is in defiance of the Rugby Football Union’s ticket terms and conditions.
Those terms and conditions stipulate any unwanted tickets must only be sold on only via the RFU’s official online ticket exchange.
An RFU spokeswoman told Telegraph Sport: “The England v Ireland match at Twickenham is sold out, and has been for a long time. There is huge interest in the match.
“Our stance on the secondary market is very clear – Twickenham tickets cannot be sold on secondary websites. It is a clear breach of our ticketing terms and conditions, and we are constantly monitoring the marketplace.
“Our message to rugby fans is clear – don’t risk your money by purchasing tickets from a secondary site because if you do, there is a good chance you won’t be able to get in.
“As ever, we want tickets to go to rugby fans who want to come to the match – and not to people who want to trade them as a commodity.”