I really am horrified by some of the posters on here who think assault and theft is justified by a social meeting.
The date was a social event to which no set rules apply. You can see that from the confusion over who should pay. While he clearly expected half payment, she had different expectations and the rules weren't clearly set out in advance, so neither is in the wrong. You also ask questions such as whose choice was it to go to such an expensive bar, buy such expensive drinks and whether she drunk them or if the date was so unsuccessful, she spent the evening trying to get away. However by paying, the immediate bill was settled and this does not create an equally immediate right to self-determined and forced compensation. His remedy in law would have been to sue her for half payment. And the Blackberry is worse more than £25, never mind the assault (putting her in a state of fear and alarm).
I would also question his motives - some men treat women like prostitutes, and equate taking them with an expensive bar and buying them a couple of drinks to expecting them to go home with them and have sex. Its a complete overreaction to what happened on the man's part. If half payment was really so important to him, he should have set out the "rules" of the date in advance.