The most difficult bit of the task was to get the new bed level and properly lined-up with the others. After a certain amount of judicious raking, shovelling, backfilling and thumping, and with the aid of tape-measure and spirit-level I finally got the timber bedded-in to my satisfaction.
The pieces of timber are held together with steel angle-brackets. I used an electric drill to start off the screw-holes, and then put the screws in with a manual screwdriver. I have found that my electric screwdriver doesn't have the power to insert the 2.5-inch screws into this tough timber. The upper layer of baulks is fixed to the lower layer with a pair of straight 6" brackets, one of which you can see in the photo below at the mid-point of the long side of the bed.
Now I have the task of filling the bed. The soil from the old bed is going to form the bottom layer. Then I am going to add the contents of one of my plastic compost-bins. At this stage I will also add some pelleted chicken manure. Finally I will add a layer of the loam that I bought a few weeks ago. With all that, I ought to be able to grow some decent veggies I think!
I have left 50cm between the new bed and the older one next to it, and in this gap I have laid a layer of 25mm shingle to match the rest of the garden.
Now I have a dilemma. I have enough timber to make one more bed of this pattern - or TWO single-layer beds.... All of the remaining three existing beds are in dire need of replacement, (one is just a pile of soil now) and it might be more sensible to take the second option. After all, it would be easy enough to add the second tier at a later date. I'm going to have think about this.