ben_short on Twitter, has asked TopVeg “any advice on avoiding creating a surface pan when watering a newly planted seed bed?”
This is a very interesting question, which requires a longer answer than the 140 characters allowed on Twitter!

water
1. Give small droplets of water – using a very fine rose on a watering can, or a spray. This will not swill the surface like water from a hose pipe
2. Retain small cloddy bits of soil on the surface, to help keep it open. It is good to have fine soil around the seed to give plenty of soil/seed contact. The seed can then take the water from the soil & start to grow. But the surface of the seedbed should contain little lumps of soil, so that it is not a powder which will soak up water & then dry into a hard sheet or cap.

water-seeds-in
3. When raking the seedbed do not collect up all the small bits and clods to leave totally fine soil. Fine, powdery soil will run together when wetted, & then go solid when it dries out.

rake-seed-bed
4. Do not overwork the soil, leaving a very fine soil on the top. The fine soil will go hard after a wet & a dry. The germinating shoot will not be able to push through this hard cap.
5. On clay/loamy soils, sow seed into moist (not wet) conditions. Before watering the seeds in, let the surface of the soil dry out a little so that the small cloddy particles go hard. Then they will repel water and not melt when wetted.
6. Be careful not to over water and make the soil water- logged. Too much water will fill all the air spaces – pushing all the oxygen out of the soil. It is better to water little & often, maintaining a permanently moist (not wet) soil.
Watering a newly planted seed bed requires lots of attention to detail!