Tempo training

Can some one please tell me how I should be running a tempo training session correctly. I have started running again in September after a 10 year lay off and upto 30miles per week and would like to introduce speed training into my training programe. When doing a 40 min tempo run should I maintain a constant speed at 10k pace or should I be increasing the speed during the run to a peak and maintaining it for how long?
Your help is much appreciated
G.

I'm not too sure about tempo running but I think it varies depending on what you're training for.

I believe you should hold the pace you're aiming for rather than increae it. As it's not a speed session and you should feel capable to of doing the distance again once you've finnished.

I think of tempo runs as speed training practising the pace you're eventually wanting to race, and holding that pace fairly consistently for a period of time, as opposed to speeding up. If you're training for a 10K race, 40 mins sounds quite a long time at 10 K pace, unless that included a mile warm up/warm down.

I'm currently using tempo runs for 1/2 marathon training with good effect, usually do 8 miles at or slightly faster than my target race pace. In theory you should cool down at the end with 1-2 slow miles, but I tend to skip that out of impatience.

I usually do a mile or so slowly to warm up, then a mile speeding up, then 4-5 miles or 30-40 minutes (dending on what i'm training for) at speed (too fast to hold a conversation, but slow enough to gasp out short sentences), then do a mile or so slow down/cool down.

Thank you for the advice P.M,L.L and D.S. Iam training for the London and it seems that 40mins at 10k pace is a little fast. Thanks again
G.