Of course I was immediately suspicious.
1. Never heard of them
2. As you can see from the Euromillions results in this blog, 2nd prize is always in the hundreds of thousands or millions of Pounds!
3. He never bought a ticket.
A quick Google search on IWG Euromillions brought up several sites pointing out that it's a scam.
If you have received a letter from them, it looks like you should just bin it. Definitely don't send them any money or credit card details.
Don't be scammed. Do your research.