How to remove the old kitchen tap

Isn’t there a gap between the the sink bowl and the back of the unit - where those flexi tap hoses are?

 

I think the tool you need is called a basin wrench.

Short video on how to use one here.

Having used one of these a couple of times I think I can say it's one of the reasons that good plumbers are worth every penny they earn.

 

You need 10mm or 12mm box spanner to undo nut on tap turn off valve undo flex’s then pull tap out some times it’s easier to remove bason

 

https://www.screwfix.com/p/basin-wrench-15-22mm/13294

 

Given that the tap has flex hoses (not cables) for the hot and cold supply then:
1. The body of the tap will almost certainly be secured with one or two 10 / 12 mm nuts on one or two threaded studs. The studs will pass through a "horseshoe" washer.
2. To undo those will require a box spanner as suggested by ginger tuffs. Something like Screwfix 6057H.
3. Neither of the basin wrenches suggested by vrDrew63 or MRY are likely to be useful, unless it is one of the relatively rare taps with a single large securing nut.
4. If you can't see where the flexi hoses enter the body of the tap, you have no option but to cut away and remove the top part of the back panel. You can always repair it after the job is done, and make the repair removable ready for the next time.