You should have been informed of your state pension before you got to 65.
Then you can decide to take the pension and continue working or defer the state pension to a later date. Not sure but I think you can only defer the state pension for 5 years so if you are not getting it you will have to take it next year at 70. If you take it or defer it is up to you but you do need advice on what is the best option in your situation. I assume you have got the exemption from paying National insurance sorted , as you do not have to pay that after 65. You do not need to tell the tax man they will just tax you or not according to your income , pension, work or a combination of the 2.
I would just add that in most cases it is more beneficial to take your full state pension as soon as possible even if you pay tax on it by still working.
The amount you gain by deferring your state pension is less than you lose in tax on it when working.