if neighbours workmen damage my shrubs whilst repairing their fence, are they responsible for replacing them?

Yes

You might win a claim in court, but don't be so awkward. The neighbour replacing a fence should be an advantage to both of you. Very few plants will suffer any damage, especially at this time of year. Cut out any damaged branches and most plants grow back even better.

Yes, they are, but many shrubs will recover is trimmed right down so it is difficult often to come to an agreement on this issue. Your costs to pursue a case will be more than the cost of replacement shrubs.

Yes they are. They have committed trespass with damages and are responsible for putting it right. If they refuse get a quote for repairing the damage and take them through the small claims court.

Yes, they are deffinately.