That expected delivery date should be clearly listed on the item listing. After purchase it should not change if it does, you refer to the original estimated date on the listing and carry out an item not received case later, if necessary.
A month's delivery will show the seller is based in China and that their items will be coming from China, location should state this and not UK.
However, the location only describes where the item is and many Chinese sellers use forwarding Companies here in the UK to facilitate a faster dispatch. Here. you do have to go to the seller's profile and check their country of registration then make your decision to buy or not to buy.
@mwatts3430