My petrol gauge was about half way in the red this morning, i put £10 in and the gauge jumped to half a tank, that has now dropped to 1/4 tank after 25 miles. Is there something wrong with it?

They're not really that accurate. If it costs roughly £40 to fill a fabia @ £1/l of diesel, then £10 should be roughly 1/4 tank. I don't pay a huge amount of attention to mine until the light/warning bleep come on.