http://www.legislation.gov.uk/id/uksi/2021/557

Service of documents9.

After Rule 101 insert—

“Deemed service101A.
A document sent or delivered in accordance with these Rules by a method specified in the first column of the following table is deemed to be received on the day specified in the second column—
Method
Deemed date
First class post
The second day after the document was posted or left with, delivered to or collected by the relevant service provider or, if that second day is not a business day, the next business day after that second day.
Delivery to or leaving at proper address
If the document is delivered or left before 4.30pm on a business day, that day, or in any other case, the next business day.
Document exchange
The second day after the document was left with, delivered to or collected by the relevant service provider or, if that second day is not a business day, the next business day after that second day.
Electronic means (where directed under Rule 101(1)(d))
If the document is sent before 4.30pm on a business day, that day, or in any other case, the next business day.”

Method	Deemed date
First class post	The second day after the document was posted or left with, delivered to or collected by the relevant service provider or, if that second day is not a business day, the next business day after that second day.
Delivery to or leaving at proper address	If the document is delivered or left before 4.30pm on a business day, that day, or in any other case, the next business day.
Document exchange	The second day after the document was left with, delivered to or collected by the relevant service provider or, if that second day is not a business day, the next business day after that second day.
Electronic means (where directed under Rule 101(1)(d))	If the document is sent before 4.30pm on a business day, that day, or in any other case, the next business day.”