You can buy a second hand / new flip key fob and set up the Remote central Locking using your spare key in the ignition. (they can be £20-30). Then you can get a blade cut on eBay from a photo of your spare key blade (£10)
Then you would need to split the spare and take the transponder chip out and put it into a new flip key body so the immobiliser would de-activate.
This will get you a new flip key... but you'll still only have 1 key.
The alternative is having a second (new) transponder chip added to the secure key list in the cars ECU. For this it's probably worth paying someone like the guy above to have this done rather than mucking about in the ECU. There's various stories of success / failure doing it DIY.
I created a second flip key for my
Mk4 Ibiza from the first method I mentioned.