This info was posted in the thread I mentioned earlier (originally posted by PPRUNE RADAR)......
In the UK, the CAA offer the following advice (as correctly mentioned by DX) in AIC 97/2004:
BLOOD, PLASMA AND BONE MARROW DONATION - FLYING AND AIR TRAFFIC CONTROL
1 Many aircrew and controllers have expressed the wish to donate blood in support of the National Blood Transfusion Service.Blood donation is invariably a safe, painless and uneventful procedure and the blood volume is restored within a few hours by redistribution of body fluids and intake of soft drinks and beverages. A few individuals feel faint afterwards but this effect is minimised by resting supine for a short time (15-20 minutes). Donations are not taken from those found to be anaemic.
2 Blood and Plasma Donation
2.1 Aircrew
2.1.1 Aircrew are advised that in order to prevent the very slight risk of post-transfusion faintness or syncope they should refrain from donating blood or plasma if they are required to fly within twenty four hours.
2.2 Air Traffic Controllers
2.2.1 Air Traffic Controllers are advised to avoid donating blood if they are going on operational duties within a minimum of twelve hours. They can, however, give blood when coming off shift.
3 Bone Marrow Donation
3.1 After bone marrow donation which involves a general anaesthetic, the minimum interval recommended before duty for both aircrew and controllers is forty eight hours. However, the individual response to this procedure varies and specialist medical opinion should thus be sought.
Again, the thread is
http://www.pprune.org/forums/showthread.php?t=198195
Presumably, the information posted by PPRUNE radar is available on the CAA website.
doubledolphins: Perhaps it's not allowable for Navy pilots to give blood, but it may be OK for Civvy pilots to give blood.