Yeah, same here (Midlands.) September has always been nice. Obviously not as hot as June, July, and August, but nice. Easily 15C to 20C on average, (some days) even at the end. We sometimes go on holiday at the end of September, (in the UK, Lake District, or Peak District or North Wales,) and it's always nice.
I am sometimes walking around with jeans and a sleeveless T-shirt on, no umbrella, and sandals. Cool at night though. Like 8 degrees C windchill/10 or 11 temperature. Doesn't usually rain. We went away 7-13 of September several years ago, and on a couple of the days it was 22-23C.
Also, Halloween has been warm for about a decade now (and 'Bonfire Night'.) I was walking around the town last November without anything on top other than a bra and a short sleeved t-shirt, and it was the middle of November.
Some people - women mostly (wrapped in 5 layers, including a huge winter coat, a bobble hat, and gloves,) were looking at me as if I was bonkers, and asking 'aren't you COLD?!' NO! it's 18 degrees C. You don't need to wrap up in November if it's 18 bloody degrees C Margaret! I would have suffocated in some of the outfits some people had on!
I will agree though (with some) that the Autumn months (October and November especially,) used to be colder than it is now. But as others have said, it seems to be really cold in January and February now. It's like the seasons have adjusted or moved about or something!!! The temperature is due to be 18C today too! Like I said, it was last year too (in November,) but I don't recall temperatures at this time of year being so mild, til quite recently (last 10-12 years.) It was definitely colder pre 2010s... I still maintain that September has always been quite OK though. More like 'end of Summer' rather than Autumn...
I don't know where the posters live who are claiming it's 2 degrees C right now. Even in Wick in Scotland (almost at the top of the UK) it's 8 C!