Maybe it's a glitch, because I can get it and I think the terms and conditions still say it's available. Hopefully it will return swiftly for you

Nope. It's permanent. Here's a screenshot from my attempt yet again to list a small item - large letter, under 100g, and there's no option for custom delivery. Saying that small items under £10 and 100g are not necessarily eligible for simple delivery is a lie. This proves it. Actually - under "package size", Large letter UP TO 1KG is the only option here - no way to choose "under 100g".  The Large letter cost, as you can see, is £2.72. Royal Mail price, when paying online and printing your own label, is £1.55 second class, and even tracked 48 is only £2.70

You're shafted all the way now. 

YES - COMPLAIN - I did. If everyone complained and threatened to abandon eBay, they'd have to change things!

what category was this in? do they only offer for certain categories? not looked further than postcards and I can still get it for postcards ... pause... but as a trial I started a listing for something I do have that would fit in letter post, a silk hankie, and you can't do it for that category.
It is frustrating that when you opt to only use RM (in my case because evri drop off is too far away) the large letter is 2p more expensive.

The workaround I'm still using, devised by Rick, has meant I have a number of custom postage listings. I created postage policies (under

business policies) for all my items which made the workaround easier to use. It can take a few attempts to revise listings before it gives me the desired result.

Clearly you are a business seller with eBay, and I am a private individual seller. I don’t intend to become a business seller, so it doesn’t help.

If you are making things to sell, which you clearly are, you need to register as a business seller.

Your customers are being charged more than they actually should be.

You don't have to be a business seller to use business postal policies.

I have gone through all the relevant pages of "my account" setup. The only time that it shows any options, it asks me to set up a postage policy  and when the postage options pop up, all are referring to International delivery - and I only deliver to the UK.  So it would appear that this is not applicable to me. 

I'll leave eBay to those who can sell as business sellers, and try elsewhere.

Just work from your listing page. No need for your account page.

Follow my instructions exactly - https://community.ebay.co.uk/t5/Seller-Central/How-do-you-list-anything-bigger-than-61cm-Part-two/m-...

create your postage policy by clicking on the 3 dots to the right of postage policy ( underneath delivery details ) ( this workaround was a rush job as I had important things to do and I didn't spell out exactly how to create the policy)

Info was added at message 57 as can't edit original.

I am a private seller. You don't have to be a business seller to use 'business policies'

Tried that. Created a postage policy. Then got this:

Still have Simple Delivery.... No idea what's going on. Totally fed up with it all.

You need to do more than that to get a result. Follow the instructions in the link. This includes increasing your price to say £800 and setting weight and dimensions of parcel to say 41kg and 121cm by 81cm by 81cm. Then setting price back to what you want. I have postage policies for large letters under 100g, 101-250g, 251-500g, 501-1000g. Also small parcels to 2kg, medium to 2kg etc. My parcels are with simple as the price saves buyers 7p on small parcel. 

I'm sure YOU know what you're talking about, and maybe it does work, but to me it's as clear as mud.

The main point I'd make is that NONE of this should be necessary. They should NOT have made SD compulsory. Whay was wrong with the way things were? I know - they just wanted to grab more money off everyone. Well, I don't need to sell to make a living, so I'm leaving altogether. As I'm 74 I don't have enough life left to spend it dealing with this kind of sh*t. I'm off this forum too. Goodbye.