In the UK plug-top fuses are available with current ratings of: 1, 2, 3, 5, 7, 10, & 13Amps
You will usually get by with 3, 5 and 13Amp fuses.
To decide the appropriate fuse divide the wattage by the voltage - for instance, a 60W table lamp into a wall socket with a square pin plug 60Watts ÷ 240Volts = ¼Amp so you should ideally use a 1Amp fuse - You don't have one in your box so use the next one up.
2.8kW kettle 2800W ÷ 240V = 11.7A so use 13 A fuse
800W appliance at 240V = 3.33A so use a 5A fuse.
European legislation has now made the UK officially 230V ± rather than 240V.
Peccavi
April 2009