"During manoeuvring for an approach,when the situation dictates an earlier than normal speed reduction,the use of flaps 10 with gear up is acceptable."
You say the speed was a little high at F5; i.e. it was above the green bug for your weight, but it was not too high for the flap itself. I assume this was the scenario and the speed was not increasing. F5 idle thrust will hold a 3' glide path and thus not slow you down. The next action I assume was going to be gear down F15 about 4nm out. I don't know your weight, but I guess you were about 10kts too fast. So why not put the gear down at 5nm? That'll achieve you being at the correct speed for F15 at 4nm and use less fuel than dangling the Dunlops too early. There was no need to panic. F10, with the LED's going to full ext is perfectly acceptable, and is a good way to lose 10-15kts in 3-4nm. However, if your captain wanted to slow down 10kts in 3nm why not use that which is designed to do it = speed brakes. OK, I know, they are not too effective at slow speeds, but they will work over 3nm for such small adjustments. They are variable drag, while the gear is fixed drag. Once down it is down. Too early means more fuel & noise.
note: if at 7nm you are high & fast and not sure if your increased ROD at F5 (V/S and thus speed increase) will save the day, then gear is a great idea. I find too many low hour F/O's reluctant to use it thinking they'll get away with it by 500'. Their neck hairs have not yet become prickly enough. When they do start to twitch it is often too late.