Managing personal Outlook.com account settings, security, and privacy
Hello IanHetherington1
I hate to be the bearer of bad news but once an alias has been removed - the action is permanent. That address can never be recovered/reused again as per the notice in that attached screenshot that is displayed. There is no 30 day recovery period for an alias email address.
Outlook MVP Diane Poremsky has created a UserVoice suggestion regarding the recovery of alias addresses which you might want to vote on but unfortunately it won't help you today.
Recover deleted outlook.com aliases
https://outlook.uservoice.com/forums/601444-the...
Regarding >>If I can never recover thehotmail.co.uk alias, is there some way I can continue to receive emails through theoutlook.com alias. as it is currently not allowing this.<<
If by that, you're asking "can I still get email using the old alias address?" - the answer is also no.
Note: This is a user-to-user support forum. We're users just like you helping other users who don't work for Microsoft and have no input to Microsoft policies and procedures. There is nothing we can do since no one in the forum has any access to any user account. Can only provide the information applicable to the question/issue posed.