Rather than operating autonomously and squawking conspicuity (7000 or 2000), you are encouraged to select the most relevant Frequency Monitoring Code (FMC), colloquially known as a Listening Squawk, of the nearest appropriate ATSU to indicate that you are monitoring that unit’s frequency. By doing so you will develop situational awareness of traffic under a service and also traffic landing at, or departing from, the airport that the CAS serves you will also get updates on the relevant QNH and may hear warnings of developing/changing weather. When you are operating close to controlled airspace (CAS) and operating autonomously, it is good practice to monitor the relevant ATC frequency. On occasions obtaining a LARS may not be possible either due to the geographical location of the flight or time of your flight or indeed it may just not be wanted. It is always good to obtain a service from a Lower Airspace Radar Service (LARS) unit for a variety of reasons ranging from traffic avoidance/warnings through navigational assistance to a ‘comfort blanket’.
The suite of services available are detailed in CAP774: UK Flight Information Services. As part of your planning it is essential that you know which Air Traffic Service Units (ATSU) are available along the route, what they can offer you and consider what you want from them.