1. There is no such allowance.
2. Every Accident-on-Duty must be investigated and probably details returned as to the "seriousness", how it occurred and the steps taken to rectify (Incident Report Form).
3. You may be entitled not to have the sick leave due to the accident counted over the one year and four year "read-backs" regarding half and nil-rate-of-pay. As far as I know there is a 3 month limit on this sick leave.
4. There is a possibility that while you are on sick leave that you may be entitled to the Overtime, Night Duty Allowance, Saturday Allowance, Sunday Premium for which you would have been rostered.
All of the above is considered bearing in mind how the accident occurred, your line manager's report etc.