They are unlikely to work together unless they work to the same standard. They will also interfere with each other, if used in the same house.
Why do you need to use two different sets?
Normally you would have one set to extend the broadband from the home hub to a TV or vision box.
If you have any other devices at that location, you would use an Ethernet switch.
i am using 2 extra routers to extend my wifi
What do you mean by routers? The only router is the home hub, the Bt Broadband Extender Flex 500 are broadband extenders.
What are you using the Powergrid ones for?
i have 3 ip cameras that arent wifi compatible and are going to be put in different areas or my house and garden so i wanted to use powerline adapters but if i did that i could only have 2 cameras because the powerline adapters are used in pairs so thats why i wanted to know if i could link them all together so that theres 1 powerline connected to my router and the other 3 connected to the cameras??
If they are all of the same make and model, then you only need one at the hom hub as the master (AP), and all of the others are slaved off it.
If you get the BT ones, you can connect up to 10 (?) extenders, I think I read somewhere.
I don't know about getting different brands to work together. Have you changed the network password for all the powerline adapters to be the same? You can access this on the BT Home Hotspots by typing its IP address into your browser, then accessing the "Powerline" tab. Here's what the Help says:
All BT Broadband Extenders, including the Wi-Fi Home Hotspot support the HomePlug AV standard and are compatible with one and other. They can also connect to other Powerline devices supporting standard.
For these devices to communicate on the same network, they must all use the same network password. BT Broadband Extenders are pre-set with a unique network password for maximum security. You change this password either by entering a new value in the Network Password field, alternatively they can be easily synchronised using the “Link” button – please refer to the user guide for further information."