Visit the Shut up about Barclay Perkins site

Unwise things to do when in a foreign country, number 238: toasting to the destruction of that country in a public place.

You must be a particularly stupid, arrogant or pissed foreign visitor to pull this stunt. I'm surprised they got out alive.

The German Toast in London Causes Disorder
On Saturday evening (says the "Standard") a party of Germans were seated at a table in a restaurant in Leicester-square London. They were drinking lager beer freely, and as they began each fresh glass solemnly touched glasses and said, "Health to the Kaiser, success to the Germans; to England, death and damnation." Englishmen listened with anger and disgust, and at last an elderly man walked up to the table swept glasses and beer to the floor with a heavy walking-stick, and administered a good thrashing to some of the company.

The Germans picked up their hats and bolted to avoid further punishment. They forgot to pay for the beer which they had consumed, and as the Englishman who had put them to flight refused to pay for the damage the proprietor had to bear the double loss himself.

At another and perhaps better-known resort in Coventry-street, where several groups of foreigners were drinking the Kaiser's health, something like a riot resulted. A party of Englishmen raided the tables, and a strenuous free fight was soon in full swing. Fists, walking-sticks, and umbrellas were used as weapons, and electric light globes, glasses, and chairs were smashed to atoms. The Germans got very much the worst of it, and were only delivered when the manager of the place and several waiters intervened, and requested the Englishmen to leave."
Western Times - Tuesday 25 August 1914, page 2.
It's odd they way Lager Beer is mentioned by name. They could have just said that they'd been drinking or had been drinking beer. Why mention it was Lager Beer? Presumably because it was seen as something foreign.

I doubt an incident like this could have happened much later, simply because tehere wouldn't have been Germans running around loose in London. They'd have been locked up or kicked out. This was still very early in the war, Britain only having joined in on 4th August. The mood in Britain later became so hostile to Germans that anyone with a vaguely German-sounding name risked attack.