I'm not a gastropod expert! and the picure ist not the best, but this specimen should belong to the genus Gibbula - I guess this is a juvenile specimen of Gibbula umbilicalis (which is common in European waters), overgrown by some kind of algae.

(quick image search for "british marine gastropods")

Best regards

Michael

it seems the same to me!

best

Fereidoun

it is a youth of Gibbula, it resembles to the Gibbula umbilicalis (Costa, 1778), but it distinguishes him to possess a great number of spiral cords on the back of the coils... I consider it a  youth specimen of Gibbula cineraria (Linneaus, 1758)

Best regards

Ermanno

It's a yuong Gibbula maybe a Gibbula umbilicalis (Costa, 1778)

Sofie these links may help you.....  

1) http://www.idscaro.net/sci/01_coll/plates/gastro/pl_trochidae_1.htm

2) https://www.flickr.com/photos/56388191@N08/9871482474/

3)http://www.flickriver.com/photos/tags/gibbulaumbilicalis/interesting/

Regards 

sachin

Thanks to all of you for your suggestions! very helpful

Gibbula cineraria (Linneaus, 1758)  -  Rondstone (Ireland)

Gibbula umbilicalis (Costa, 1778)  -  Port Luis , Bretagne (France) ......   :-)

Ermanno, does Gibbula umbilicalis have the little umbilicus also in very juvenile stage?

Maria Martina, juvenile of Gibbula umbilicalis possess an ample umbilicus and a very strong spiral sculpture, while in Gibbula cinararia the umbilicus is more tightened and the spiral sculpture is thinner and with a great number of cords. I attach you a photo with three exemplary juvenis of Gibbula, seen by the side of the umbilicus... the two in low they are of G.umbilicalis, that aloft to the right of G.cineraria. Great Specimen = D. 4 mm

It seems a Gibbula cineraria, as pointed in other comments