I thought I'd update you...
I found a website which showed step-by-step instructions & pictures for removing the laptop keyboard. Following these, I took out the keyboard, removed the spacebar key and thoroughly cleaned under the silicon layer using an isopropyl/water mix. I then left it to dry for a day and put it back.
I have just switched on again and, voila! My Spacebar is working again - yippee. There must have been something preventing contact.
Thank you for your help. Hopefully, the problem won't re-occur.