RunnerG, I hadn't run a 5k or 10k for a couple of years due, mainly due to injury. Prior to that my 5k time was bang on 20 mins and my 10k time 40 mins 20 secs.
As part of of VLM training I ran a low key local 5k without any real speedwork training. I came home in 19.33 and that was without warming up properly.
I think the key to me running faster is down to the tempo/speed sessions I've been doing as part of the marathon training.
A key session for me is a run of between 8 and 12 miles where I will build in speedwork. The first 3 miles will be warm up, slowly getting to a tempo pace and then each mile will be quicker until I'm flat out on the penultimate mile, using the last mile to cool down.
This meant that I was able to use that tactic in the 5k race and whilst I was panting at the end I finished feeling like I could go faster.
After having a disasterous marathon last week my next goal is to dip under 40 mins in June for 10k and once I'm back to full training in a week or so's time then I'll be factoring in my 'long' speed session.