Intervals?

Try 30s fast, 1m30 recovery.

Shona, good to hear you're keen to press on, but i'd probably recommending getting fitter through more easy paced running first. There's a fair amount of race improvement to come from this step alone at first.

Think of easy mileage as the foundations, and think of the speedwork as the roof.

you're trying to put the roof on before you've laid strong foundations!

If you're currently doing 3 runs a week of 5k, say 9miles a week, i'd just gently add a bit of mileage progressively for a couple of months.

If you have access to a stationary cycle or a swimming pool, maybe that would help things along too as an extra session.

Over this time, you'll lose a bit of weight, and develop some kind of base. I'm certain this would show in your race times already.

I wouldn't worry about intervals until you're comfortably handling 20miles a week personally.

If you haven't got a running base, what are you trying to delve into when you try faster running? The answer is an empty tank!

Key stuff to start doing is preventative stretching after a run. And also developing an awareness of how things are feeling. This is something that'll be very important as the mileage increases.

I agree with Stevie on this one.

Focus on time running rather than intensity. There's huge improvements to be made just off easy running.

The intervals you've described sound more like strides, E.g. running quickly for short bursts to practice your running form. Intervals tend to be anything from 200m up to 1600m and you usually do enough in a session to add up to around 3 - 5k. 

You don't need to do any speedwork until you've built up a base as you should improve during this period anyway. Once you feel ready I'd recommend starting with a tempo run. Make 1k in the middle of a normal run 30-60s quicker than your normal pace. You can then gradually build up the distance of the tempo section.

I've been told they can help with weight loss - something about burning more calories than double the same overall time plodding.  Don't know if it's true of-course, but sounds good!  Think I might leave it till I'm covering a bit more ground though.

20 miles a week though?  Seriously?  That's more than 3 runs of 10k a week!  I mean, obviously having read around on this forum I know people do, but not people like me (job, children, late 30s, overweight....).  Mind you, I couldn't previously see myself seriously contemplating a 5k run...

20miles is a benchmark figure, of course you could try intervals sooner (like you did), but you have to question the benefit.

To me, doing intervals before you have any kind of base fitness is ill advised.

I agree that you should just focus on putting in the time running at the moment but I think you could start to give intervals a go if you want. The key is not to try to do too much too soon. Try putting in a few faster sections into one of your 5k runs and give yourself more recovery time - 30 seconds to recover from a 30sec interval isn't really enough, or try doing a tempo run as Andy D suggested. Good luck and well done for getting to 5k!!

Agree with the general tone - no need to do intervals unless you want to - and if you do want to there is no need to do them quite so hard. 

One thing you could try to develop speed is maybe do a mile or half mile faster in the middle of one of your training runs - doesn't have to be flat out just faster than the rest of the run.   If you can find a long stretch of road which is gently downhill that would be a good place to do it.   

Maybe work on a quicker cadence (number of steps per minute) with a shorter stride (if you don't already). This will help you get used to moving your feet quickly without causing yourself an injury from over working. Then when you're ready you can work on lengthening your stride to cover more ground faster. But that's not important right now. But I do think a lot of beginners (I've only been running 6 months myself but am up to 18-20 miles a week), benefit a lot from working on their cadence and running 'lighter' on their feet.

I ran my 1st 5km in late December. I have now managed 10 miles on one occasion. My 5km was stuck for a few weeks until I started working on form and speed. Hill sessions have recently really helped to the point where this saturday I took a minute off my 5km time just like that, out of the blue. So keep at it. The time will improve eventually. Also bear in mind that more distance doesn't always equal better speed at shorter distances.