Why were my mashed potatoes gross?

[Turaco]

It's easy to make good mash, right?
Use floury potatoes, cut up and boil until cooked but not overcooked, drain very well and allow the steam to evaporate off, mash with plenty of butter and salt and pepper. Lovely mash.
Except that's exactly what I did, and my mash was wet and sloppy, a bit gluey, and had a weird sweet taste? It was nasty frankly.
Did I do something wrong, or (as I suspect) is there something up with potatoes these days? I had this issue last time i made mash as well. Always used to make lovely mash doing exactly as I have this time.
Spuds are standard Morrisons white floury potatoes.
Any suggestions?

I cook mine to the point they're falling apart. And as pp said, use cold water or they won't cook evenly. You're probably over mashing because they're lumpy because they're not cooked enough! It shouldn't take any effort to mash them at all.

Always store in a cool dark place. Not a fridge.
King Edward’s always work for me, and if I can’t get them I go for Albert Bartlet Roosters.
Also, I always rinse potatoes after peeling to get rid of starch.

For my special Christmas Day mash, I add double cream alongside the butter etc. and when it's all mashed and creamy, transfer it to a casserole dish and put it in the oven for 20 mins, the 'twice cooking' really brings out the flavour.

dont forget to take them out of the plastic op

Ah balls, that's where I've been going wrong

I leave the steam - it helps the butter melt into the potato’s
never used floury potatoes, didn’t know they were a thing.

The excessively wet summer means potatoes are crap this year

A couple of bottles of cider on an empty stomach!

The potatoes had a high sugar content. Late crop. They were over mashed to go gluey

Don’t keep potatoes in the fridge or in a plastic bag. They need to be in a cool, dry dark place (easier said than done in many houses). I can taste the difference when potatoes have been stored too cold, our local Sainsbury’s used to be guilty of this.

Probably teaching nana to suck eggs... but... Maris Piper always here for nice mash. Kept in a cupboard (in the plastic bag they come in... they aren't kept long enough for that to matter here)

When you've drained, leave lid off, add tons of butter whilst spuds are hot, splash of milk, salt and black pepper, mash just until no lumps.