a) a 2-gang 13A cannot draw more than a nominal 26A because of the fuses in BS 1363-1 plugs
not at all sure about that. Just how long will a standard BS1362 fuse take to open if it is carrying say 16A? How long if it was in use outside in these currently freezing temperatures? If you can't get more than 26A out of a double gang socket then you aren't trying hard enough. A word of warning: not all 13A dual gang outlets take kindly to running at 26A.
Don't try this on your house wiring: use a test bed. As much as it ought to be safe it is an expensive experiment if the house wiring isn't as good as it should be.
[can't find a characteristic curve for a BS1362 fuse must have filed the info somewhere probably up in the loft]