How do you deal with people who are always late?

We have a particular couple of friends who are always late.
We arranged to meet on holiday and they said they would be with us lunchtime. We waited and waited, and they eventually arrived at 4.30pm (they were coming by car, so no flight etc)
Today they are coming to our home, said they would be with us at lunchtime. I have made food for them, which is now ready. Just received a call to say they won’t be with us until 1.30–2.00pm.
How can I politely tell them their behaviour is not acceptable?