I blocked mine as well from the accessing the internet.
I blocked it in my router
Gave them a static ip address and blocked that in my router.
I have one new in the box too but donāt want to link it to my account in case it applys a firmware update. I guess it needs internet access to register with your account or can it register without internet access?
I donāt think I can do that on my bt hub 
@Jamezz98, I honestly canāt remember if you need the app/account to set it up or not. My gut feeling says yes though. 
I replaced my bt home hub ages ago so canāt check, but https://community.bt.com/t5/Home-setup-Wi-Fi-network/Restrict-internet-access-for-a-device/td-p/1989323 suggests itās not easily doable.
Yeah, I saw that and all I thought was āfine, give me the non easy way then!!ā The options further down werenāt helpful either. Oh well. Guess Iāll continue to bug tp-link customer service instead.
I believe (because it worked while I was diagnosing my original problem and did a factory reset of my plug) that you can set up a new device with the Kasa app while the device is unable to reach the internet, so long as the phone running the app can sign in as normal.
The BT hub is crap for configurability, but you might be able to temporarily block the plug using the parental controls? As I recall mine wouldnāt let me block any device permanently though. Which is why I now own a better router.
No response from TP link to my enquiry yet, and my hopefully-esphome-compatible plugs are due to arrive from Amazon today.
The parental controls block local access as well, it complete blocks Wi-fi connections.
Tp-link answered me on Twitter, but that was the useless āit was a necessary improvement for safety, and you should only use the KASA app anyway so stuff youā type of reply. I asked them to consider at least an opt-in for local access. No response yet.
I also contacted TP-Link asking if itās possible to downgrade to the older firmware, Iām not sure if itās by design that itās now blocked from working or a bug.
I would have thought if it was by design the new firmware for the older HW revisions would have blocked access as well and it doesnāt seem to have done so.
Honestly Iām not really expecting much from TP-Link, but I figured it was worth a try.
I think itās by design, because Which?, the British consumer advice group, complained about lack of security. See my screenshot in reply 12 or something, taken from the Which? article. Thanks Which?! 
I just received a reply from TP-Link andā¦ itās an out of office notification! 
Possibly but I think itās a bit odd that the earlier HW revisions also got a firmware update yet still work with Homeassistant
I just did a test on the plugs i have here to see what is listening on different types and firmware versions.
Port scanning a HS110 with hardware version 1.0 and firmware 1.2.6 shows it has port 9999 open.
Port scanning a HS110 with hardware version 4.1 and firmware 1.1.0 shows it only have port 80 open.
So it does look like the 1.1.0 firmware on the newer hardware version of the plugs is what shuts down the 9999 local port and instead runs a webserver on port 80.
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Wonder if it uses a similar control scheme as the tapo ones.
When I have enough free time I might see If I can setup an AP connected to a switchport thatās mirrored to a machine running a packet sniffer and see if I can capture the conversation between the Kasa app and the plug.
They can still be controlled locally it seems as I blocked one from the internet and put my phone on my IOT VLAN and was able to still control it.
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Got a sensible but disappointing reply from them now.
So it looks like we were right. Bye bye TP-Link for meā¦
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No more TP-Link hardware of any kind for me!
That said, I think one point may have been missed in this discussion.
I never created an account on the TP-Link server using the Kasa app. I was able to detect and set up my HS110s from the app on my internal WiFi network. I think this means the devices were never given a Kasa account which they would need to access the TP-Link servers. At any rate, my HS110s do not appear to be auto-updating their firmware.
Within the Kasa app thereās an option to identify available firmware upgrades, and to upgrade my devices. I have not done that and the devices arenāt updating on their own.
Obviously I canāt use the Kasa app outside my network (thatās what HA is for!) but maybe not associating the devices with a Kasa account at setup time is what saved me. Maybe itāll help someone else.
Yes, I think you are correct. I didnāt have an account, so I manualy upgraded the firmware from the Kasa app. There was no notification that it was available, I checked because I was looking for a fix for the spurious power figures I was getting.
However, my other HS110s are staying in their boxes for now, just in case.
Anyone have any recommendations for UK plugs which support MQTT as an alternative?
Sonoff S31 flashed with Tasmota works great in the US. Maybe they make an equivalent for the UK?
The sonoff s26 has a UK version and is flashable with tasmota or esphome.