UK Motorway Slip Roads - Speed Limit

Short summary: There is not a universal speed limit on UK slip roads. While in general the national speed limit for motorway applies, if there is a speed limit sign stating otherwise you should follow that instead.

According to [Highway Code Rule 124](https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158?:

Rule 124

You MUST NOT exceed the maximum speed limits for the road and for your vehicle (see the speed limits table).

This means in general, the motorway national speed limit applies on slip roads (given it under motorway restrictions, see @Weather Vane's answer). However if there is a speed sign installed that indicates otherwise, that would be the actual speed limit.

The actual speed limit on a motorway then could be:

• The national speed limit, whether it be:

  • A new speed limit sign (e.g. The speed limit sign on a slip road from A720 on to M8 (J1), curiously it is showing 70mph instead of the national speed limit);
  • A sign saying it is a motorway, and hence motorway restrictions (see Highway code 253-273) apply, at the beginning at the slip road; or
  • A lack of sign when you join from a road already having a national speed limit (e.g. All 4 slip roads between the M3/M27 Junction, though advisory speed limit is sometimes in force according to Google Maps).*

• The speed limit of the motorway you are joining (e.g. this slip road joining M32 in Bristol has a speed limit of 40mph, that on that particular stretch in M32.

Or, in fact:

• Anything that they decided to show. Google Maps captured a 40mph limit specified by the variable speed limit indicator on the slip road leading to M25 Northbound in M4 J4B Westbound:

Somewhere else in Birmingham, a 30mph limit is (was?) imposed temporary on a slip road on the Spaghetti Junction due to works (A38(M) Northbound J6, leading to M6 Eastbound, Image also from Google Maps):