Under the new ownership it seems that Royal Mail have introduced longer delivery times for their 2nd Class Standard LETTER (including LARGE LETTER) Service so the current average delivery time is now 7 Working Days (Mon-Fri).
Royal Mail will not provide us with any tracking data until 10 Working Days have elapsed
The Royal Mail Tracked48 service is now 2-3 Working Days
(below is from the Royal mail website)
Royal Mail deliveries are operating as normal across the UK today. Royal Mail aim to deliver to all addresses we have mail for, six days a week. In a small number of local offices, this may temporarily not be possible due to local issues such as high levels of sick absence, resourcing, or other local factors. In those cases, we will rotate deliveries to minimize the delay to individual customers. We also provide targeted support to those offices to address their challenges and restore our service to the high standard our customers would normally receive.
You can check if your postcode area if affected by checking the Royal Mail website
Copy this web address to your internet browser (links disabled here for your security)
https://www.royalmail.com/service-update
Then click on 'Deliveries Today'