A Puzzle With Coins

I bought the prize for this competition using n coins (normal UK coins) which have total value T pence.

1. There are exactly three ways to make T pence using n coins.
2. One other way uses more round coins than I did, and the other uses less.
3. No value of coin is present in all three ways.
4. I could have made the same purchase using n+1 coins, and still satisfied conditions 1, 2 and 3.

What were the coins that I used?