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Hello Ectemnius

Thank you for answering, and I'm sorry I've been so long in responding.

I do not think that these are Myathropa florea larvae. I have checked with a key (Danish book Danmarks Svirrefluer by E. Torp) and it states that florea larvae have a much longer breathing tube (about 3 to 4 times the body length) and the front breathing horns should be paler.

There is one more possibility besides Helophilus and Eristalis, and that is Sericomyia silentis - although I only spotted a fly of this species on two occasions, whereas there has been plenty of the other two species on the site. This doesn't rule it out, though. In favour of Sericomyia silentis is the size and shape of the front breathing horns, that looks rather short and stumpy.

Sadly the quality of the images are not really good enough to clearly show the characters that I need to use the key properly.

Best regards