Running

Sounds like you already know what to do, 30s hard hill efforts or almost-all-out-sprints (90-95% efforts) will see you go anaerobic. Be sure to take the recoveries really easy.

I've been doing more speed work recently and have been following the speed sessions put together by some coaches at a local athletics club. I can't make the sessions but know someone who does who feeds them on to me. Things like pyramids (2x1 min, 2x2min, 2x3min, 2x2min, 2x1min) and mixed tempo/hard efforts (3x[3min hard/3min tempo], 5min easy, 2x[2min harder/2min tempo], 2 min easy, 4x[100m HARD, 30m easy]).

Any tips for a good type of workout to start off with?

You're around Blackheath right?
St Germans place. Run 2 sides of the triangle faster than your 5k pace, run the 3rd side easy. The first rep should probably feel a bit too easy, by the time you're on 4th, 5th, 6th then it should feel pretty tough. Pick a pace that you can maintain throughout the reps rather than going too hard at first and then slowly dying throughout

Hill
15minute warm up
8 - 10 reps of 35 seconds up and jog back down
10 min cool down

Intervals
15min warm up
12 x one minute on (say 5k pace) one minute recover (ideally jog it but walk)
10 min cool down

• with this one you can try 4 x 3 minute intervals with 1 minute rest and 4 x 1 minute intervals at faster pace with 1 minute rest.
  
  

Progression
10 mins @ 5k pace + 30%
10mins @ 5k pace + 15%
10 mins @ 5k pace
Cool down 5 mins

• with this one you can change the times so that you extend the faster ranges
  
• you can reduce to 2 longer blocks of 20 mins.