Sizing on dress patterns

This is a technical question for those people who have been dressmaking recently. I haven't made anything from a pattern for years and years: I used to make clothes for the children, but as my youngest is in her mid twenties you can tell that was a while ago! I must have got rid of my patterns when we moved 13 years ago. Partly seeing what people on the Homemade Life have been making, and also watching the BBC Sewing Bee, I decided to give it a go with an A line skirt. I ordered a pattern, and sat down yesterday to figure out what size I would be. In M&S I am a 14, or sometimes a 16. I measured my waist and hips, and was horrified to see that according to the pattern I am an 18 - 20. I am OK with altering the pattern so that the waist is one size and the hips another, but just wondered if anyone else has noticed this seismic shift in sizing!
As a PS, I have decided that the pattern is too complicated for a first return to sewing, as the waist has a series of facings, so can't be altered to fit easily. I have discovered a more straightforward one which I can play around with to make sure that the sizing is correct.

Having recently got back into dressmaking I have also discovered that pattern sizing bears no relation to shop bought clothing.  There is apparently also a big difference between makes of pattern.  Some makes are also known for allowing excessive ease.  I have always gone straight for a size 12 in the past but the recommendation now is that you check the body measurements and finished garment sizing given on the pattern envelope.  There can be a difference of two or more sizes between makes.  It might have something to do with the different countries from which the various pattern companies originate.

I am no dressmaker, so I don't know about pattern sizes, but I do know that you sell more clothes if you flatter the customer by allowing them to believe that they are somewhat slimmer than the tape measure might suggest ... This is true of mens jeans too. And it works for me; I still want to fit in the 34s

Oh I'm sure I'm a 14 rather than a 20!!

Thanks, Ploshkin - that helps. I may well use some old fabric to make a dummy skirt up, just to see how it fits.

Ah, Chilli Head, I believe the 'waist' size on men's trousers is actually the hip size so men can have a lot of excess hanging over the top & kid themselves that their waist size hasn't changed since they were 18.

Hehehe, Ploshkin.
I have some very old dress patterns - well, you never know... and have observed that the sizing on the old ones is different from more recent ones. A size 12 now is bigger than it once was and the vanity sizing that Chilli head refers to is even more prevalent in shop sizing, I believe.

I have started only using the actual body measurements on a pattern since I began buying 1950's patterns last year. According to the 1950s pattern I made last December, I am a size 16, though would be a 12 for today's clothes.

Might that be an American pattern Freebird because I think their size 16 is equivalent to our 12

Isn't it the other way round? I think US size 12 is approx. our size 16?

It is actually a Canadian pattern I believe, but Flobear is quite right, US sizes are smaller numbers than UK sizes.

Yes, my thinking was working back to front. My brain does have a tendency to flip into reverse sometimes.

Glad it's not just me, Ploshkin, my brain does a reversing thing sometimes. On the computer keyboard and the piano my left hand will do what my right hand is supposed to be doing and vice versa. Or should that be veci virsa (most often happens with e and i !)

Yay, can we have a photo?
I love the BBC sewing bee!
I have only been doing stuff for my son so no idea about women sizing.