Hi, ok, first time I've picked up a wrench, so be kind. 

My brother has a Mk5 fiesta zetec s, we thought we would try a quick service, oil in the spark plugs, looks like the rocker cover gasket has gone. While unhooking all the pipes etc we thought the fuel line that runs over the top of the engine need to come off. It looks like a regular rubber tube so we gave it, as Basil Fawlty would say "a good thrashing", It moved a bit but then we thought this might not be necessary or the best way to do it or the correct way, as there is some white catch that looks like it would pull apart. However, we have moved it back a bit from the connector. So, have we buggered it, I dont want it to leak, or is it just a case of pushing the rubber tube back all the way. It doesn't want to go so any ideas?  Do I need to be worried?

That what you pulled back is to protect the fuel line underneath from the engine heat etc . U don't need to touch that to remove the rocker casing