booking appointment for ICT T-2 extension

Hi Members

I have heard from my colleagues that there are no appointments available with UKVCAS.
Tier 2 ICT visa will expire next month. My ICT tier 2 extension is undergoing internal company approvals.

SO as soon as payment is made, I will be able to book appointments.
Can anyone please tell me about Priority appointment booking or Walk in appointments- Process, timeline and fees?

Cheers
Wesley

I searched about Priority appts and now know they cost 500 pounds.

Is there such a thing called walk in appointments?
Are they available in both Core and enhanced centres?

Thanks