Hi MangoPete:
Incidents like this are not uncommon and can be more difficult to deal with in a way which brings some form of resolution or satisfaction to all concerned, especially you as the victim.
Both Westies and Dachshunds are renowned for being feisty and snappy types of dog and can be extremely protective of "their patch" which appears to be the case here.
It does, however, not condone one of them biting you and ripping your trousers. The fact that the owners apparently spoke to the one which attacked you like it was a naughty child does depress me. A very bad example of dog ownership/
Unfortunately, because this happened on their property, it would not automatically come under dangerous dog legislation, as it would had it been in a public place.
However, it does not stop your neighbours from being held responsible, and normal Police procedure, IF you chose to make a formal complaint, would be to obtain a written statement from yourself, interview the owners under caution, report them for failing to keep their dog under proper control and give them the opportunity to sign an undertaking to keep the dog under control in the future. Should they refuse, a Court Order could be sought for destruction of the dog in question.
Should you prefer to try to resolve it more informally, but do not wish to confront the owners yourself, contact either the local Dog Warden or Police to discuss your options and it may be that they would intercede on your behalf with your neighbours. The least you deserve is an apology.
You could have a claim in any case for the damage to your trousers and perhaps even the cost of the jab, if you had to pay?
Please feel free to come back if you need anything clarified.
Good luck.