A £2 coin - blimey, that's big!
All of my cousin's dc have swallowed coins and marbles. With the first they went to A&E, had x-rays, etc, then waited anxiously for about a week for the dc to pass it. With the second they didn't go to A&E, just waited for the dc to pass the coin.
As long as the child is completely normal, no discomfort or bloating, not under the weather at all, then there is no need to worry. They won't be poisoned by the coin, the only concern is whether it causes a blockage or disturbance.
As my cousin puts it:
When your first child swallows coin you go to A&E, have x-rays, worry anxiously for a week, checking all poos, until it comes through.
When your second child swallows a coin you don't go to A&E, you just keep an eye on them and check their poos until it comes through.
When your third child swallows a coin you check their poo when you remember.
When your fourth child swallows a coin you dock it from their future pocket money.