I keep getting the flashing coolant light on the dash regardless of whether the engine is cold or hot.

Coolant level is spot on.

I have been told I need a new expansion tank which I have ordered - http://www.eurocarparts.com/ecp/c/Skoda_Fabia_1.9_2004/p/car-parts/car-cooling-parts-and-car-heating/cooling/expansion-tank/?205440680&1&1e9f95c4ca99624d5c576014204fb3d155955059&000125

Is this easy enough to swap over?

Yes its very easy a 10 minute job expect its the sender unit.

Yep, as said, it's an easy job that can be done in a few minutes.

Quick and easy guide below

http://myquickfix.co.uk/2011/10/skoda-fabia-vrs-temperature-beep-expansion-tank-replacement/

Brilliant, thanks guys. Is it worth changing the coolant whilst you are doing this?

My fabia 1.4 8v 03 started this on sunday morning so after reading alot about it on this forum i also just bought a new tank couple hours ago.

Only thing with my car is there a slight pully noise so i thought it might off been the water pump.

any ideas ppl..

Use a stick from water pump/engine/alternator to ear to check where noise is coming from. More likely to be alternator pulley/tensioner.

chears i got a tool in my tool box for doing that.

i took belt of and water pump pully has alot of play in it so orderd new one o them and belt also.