The problem with unit grades is that they're not standardized across universities, so what might be a first at a lower-tier university might be a 2:2 equivalent at a top-tier university.
Hence companies relying on A-Level scores and university reputation when filtering.
What ECs do you have ? - that's probably your best bet of getting visibility. Assuming you're a second year student you might want to apply for a GSoC on a low-level project.
ECs are Formula Student (Mostly embedded systems stuff, also did a lot of sponsorship getting organisation type stuff last year), Cyber Security Challenge UK (Got invited to a conference, have been told to keep the dates of two more face to faces clear...) and general member for one of the uni's bigger societies.
I'd recommend contributing to an open source project that aligns with your interests, as that's much more understandable and verifiable to someone reading your CV.
At the moment me and two fourth years are basically writing all the code for a single seater formula style electric race car. This means Motor controller, battery controller, HUD, sensors, telemetry and getting it all to communicate. (on the way having to learn a lot about control, signal processing and learning a new platform) Its by far the most complex system I've ever worked on and coming together really well - the guys I'm working with really know there shit.
Hence companies relying on A-Level scores and university reputation when filtering.
What ECs do you have ? - that's probably your best bet of getting visibility. Assuming you're a second year student you might want to apply for a GSoC on a low-level project.