I have a vitra toilet seat and it has come loose?

i wish i could see a picture of the exact one but toilet seats often have one of two methods to be secured

Either by means of a screw and wing nut which you can get access to the wing nut by either going under neath the toilet or getting access to the rear

some toilets seats have a cap which covers the screw or screw and wing nut.

to access the the screw to tighten it you will need to remove the cover and tighten it up often with a screw driver.
all very simple if you know how.
i hope this information was help but if you need a plumber to do it for you try
Plumbers
http://emergency-plumbers.weebly.com/
http://www.boilerguys.co.uk/

andrew t
January 2015