BEagle
If LOST, yes, absolutely tell D&D immediately and make it clear. Any other action is foolhardy and threatening flight safety.
However, if you wish to CONFIRM POSITION and my interpretation of this is that it would be a very infrequent event for each pilot, the training fix process allows this and is promulgated as such. It seems to me that it breaks a link in a potential accident chain and if used with respect, then is an excellent facility.
With the very greatest of respect, 121.5 may be an internationally recognised frequency, but in UK jurisdiction, UK agencies decide the proper use of the radio frequencies.