For what itīs worth, Norway have used radar in combined twr/app settings in low traffic situations for more than 20 years. However there was poor regulation in the beginning, and in the early 00s the union/guild had to force the regulator and ANSP to introduce some limiting regulations. (Things had gotten out of hand, controllers forced to vector sequences of 4-5 arriving aircraft while doing the twr bit as well, not good at all)
The current rules, national ammendment/addition to 4444: (I have tried to "clean" a google translated version)
Norwegian special provisions regarding the use of ATS monitoring system in the combined tower and approach control service :
1 When an ATS surveillance system used for the performance of the combined tower and approach control service in accordance with the following provisions , shall be such that the requirement for visual monitoring of traffic on and near the airport are met in accordance with paragraph 7.1.1.2 .
Availability and use of monitoring information by combined tower and approach control service shall not cause visual monitoring of traffic on and near the airport to be reduced.
When applying the combined tower and approach control service is the demands of the tower control service that will limit the scope and content of the service provided . Tower Control Service based mainly on visual monitoring of traffic on the maneuvering area and near the airport. Aircraft should only be vectored from the combined tower and approach control positions in exceptional cases.
2 Air traffic controllers performing combined tower and approach control service may use ATS surveillance system the following tasks :
a) flight path monitoring of aircraft within the air traffic controller 's area of responsibility ,
b ) the establishment of separation between aircraft within ATCO responsibility,
c ) provide navigation assistance to VFR flights ,
d ) monitoring of ground traffic as specified in section 8.10.2 and
e ) vectoring of aircraft , with the following restrictions;
i) vectoring shall not be used for more than one aircraft at a time ,
ii) vectoring may not be used while the second aircraft located in
departure phase , landing stage or in the landing pattern ,
iii ) vectoring should not be used if you also have traffic on the maneuvering area , except for cases mentioned in the fifth paragraph , vectoring shall not be used when other conditions, as defined locally, require special attention.
With the " departure phase " means the period from the aircraft commencing departure until the aircraft is in the air and passed the end of the runway . The "landing phase " means the period from the aircraft is closer than 4 NM from the threshold of runway to be used for landing until the aircraft has landed.
One can establish local procedures that allow vectoring simultaneously with limited traffic on defined parts of the maneuvering area and the necessary and limited traffic with vehicles that perform specific ground services , such as friction measurements, measurements of runway visual range and trajectory inspections.
Each ATS shall consider § 9 second paragraph a to d, according to the principles of the first paragraph and determine the maximum number of simultaneous aircraft movements permitted within the unit's area of responsibility . Furthermore, the ATC unit must assess and determine further restrictions of the second paragraph a through e , with respect to factors that controller is alone on duty , snow clearing on the maneuveringarea , reduced visibility , reduced runway friction , difficult wind conditions, operations outside daylight period or other conditions that require special attention.
3 Special VFR flights shall not be vectored unless special circumstances such as emergencies warrant.
4 When an ATS surveillance equipment used to provide navigation assistance to VFR flights special precautions must be taken so that the aircraft does not inadvertently enter IFR conditions.