How to replace front fascia light on Creda Winchester oven?

I have a Creda Winchester Multifunction oven (brown).
More than 10 years on it is still going well but the fascia light needs replacing so that i remember to switch off the oven when i have finished using it!

At great expense I bought the part from Creda (£17 including shipping - for a skinny fluorescent bulb). I have removed some screwa around the fascia but just cannot remove the glass screen to get to the light tube.

Can any one advise? This is an undercounter integrated model - single oven reference MODEL 48291

Any advice / direction much appreciated as I am now stuck with an expensive replacement part that I cannot fit!