I’ve got my brewing started. All equipment sterilised, instructions followed and measurements taken. The thick malt in the can was diluted with 4 pints of boiling water, 1kg of white cane sugar (Trade Aid brand) was dissolved in and then brought up to 5 gallons (40 pints) with cold water.
At that point I took a specific gravity reading with the hydrometer, which came out to about 1.034 at 22.5ºC (later calibrated at 1.000 at 18.3ºC). It was a little tricky to read as the beer had foam on top and I had to wait for that to go down — more care needed next time I transfer it to the measuring tube. Since everything was meticulously clean, I transferred it back to the fermenting vat.
It should take a week or so to finish this stage of fermenting, at which point the gravity should fall to 1.005 or below for at least a couple of days. According to the first online calculator I found, that should yield a brew with 3.95 ABV (alcohol by volume) although that will be higher if the final gravity is lower than 1.005. We’ll see but, with a bit of luck, I should be bottling up next weekend and able to start enjoying the results by early June.