Business subsistence on daily trip

While reasonable costs of subsistence are allowable for overnight business trips, does BIM37670 say that subsistence is claimable for, say, an occasional trip to London where a meal and some coffees and some water will be bought? The person is self-employed and returns home the same day.

I am confused by HMRC mixing the issue up in the same paragraph with 'itinerant travellers'; also what do they mean by 'the normal pattern'?

Thanks for any help.