1. When booking a room for myself and my wife the other day, the receptionist was rather rude to me.
- Corrected: The receptionist was rather rude to me when I was booking a room for myself and my wife the other day.

2. Looking at my diary, there were several double-booked appointments.
- Corrected: When I looked at my diary, I noticed there were several double-booked appointments.

3. Remember to use unleaded petrol whenever filling the tank.
- Correct (possible addition for clarity): ...whenever you are filling the tank.

4. I hope you've mentioned this to the concerned people in the matter.
- Corrected: I hope you've mentioned this to the people concerned in the matter.

5. Not having written about the required topic, the teacher gave my presentation a low mark.
- Corrected: Because I had not written about the required topic, the teacher gave my presentation a low mark.

6. It was an extremely involved story. I couldn't make head or tail of it.
- Correct

7. While working in California, my house was damaged by an earthquake.
- Corrected: While I was working in California, my house was damaged by an earthquake.

8. Being such a sunny day, I got up early and went for a swim.
- Corrected: Because it was such a sunny day, I got up early and went for a swim.

9. Judging from his expression, you're about to be disciplined!
- Corrected: Judging from his expression, he looks like he's about to discipline you!

10. Do you know anyone having been to the Canary Islands?
- Corrected: Do you know anyone who has been to the Canary Islands?

11. The employees involved will have their pay docked.
- Correct

12. The club approved of the solution adopted by the sub-committee.
- Correct

13. Whenever leaving the premises, please ensure that the security system is switched on.
- Corrected: Whenever you leave the premises, please ensure that the security system is switched on.

14. Once ensconced in his comfortable armchair, the television didn't bother him at all.
- Corrected: Once he was ensconced in his comfortable armchair, the television didn't bother him at all.