Your top mounts have delaminated. The rubber is bonded to the metal part of the mount and it's simply coming "unstuck". These mounts would fail MOT in this state and need to be replaced now.
Not a bad job to do if you have the experience and tools to do the job. Bloody dangerous for an amateur as it involves compressing the main suspension springs which means you need proper suspension compressing tools and the cheap DIY type, in inexperienced hands, could let the spring go when compressed. You can imagine, I'm sure, the springs are very strong and, if a compressor slips or comes off altogether, mayhem will ensue.
The mounts themselves will likely be available from multiple sources, I'd probably approach my local motor trade factor and I'd be surprised if he couldn't supply at a very competitive price.
It's not unusual to find additional components might benefit from being replaced once you start in on this sort of thing. The shockers may be pretty worn out and/or leaking slightly. Bump stops may be worn or missing all together, The bottom ball joint may be dodgy, etc, etc. If you're doing the job yourself price isn't too bad but if you're paying someone the price can rapidly escalate because parts are often corroded together and take time to free off.
