The best checker to use is the BT Wholesale one
, using a telephone number.
The address checker gives good results with a correct address, but the postcode checker is not always accurate (a postcode can be served by multiple cabinets).
So how did you check before?
Your cabinet might still be supplying FTTC, but BT have temporarily run out of capacity. If that happens, the checker gives results that look identical to there being no FTTC at all. Capacity problems can include the copper tie cables back to the PCP or linecards (Openreach don't fully populate the cabinets from day 1, so need to go back when capacity is needed). The cabinet could be entirely full too - in which case you need to wait for a new cabinet.
Q1: With a 10Mb prediction, it suggests you are probably over 1km away from the cabinet, or you are connected to a closer one using aluminium rather than copper.
A copper line of 300 metres would probably give a prediction of 50-60Mbps.
Other than that, I can't help with Elstree directly
Q2: Yes. Email nga.enquiries at openreach.co.uk
That should give the current situation.
Q3: There seems to be a heap of mis-understanding there, that all eventually leads to an answer of "no".
BT won't let you install your own fibre, and then make use of it as part of their own access network. If you want to make use of their access network, then you have to pay for them to provide the copper or fibre (as FTTPoD) as part of a contract with an ISP.
Their current rules for FTTPoD are that you must be served using a cabinet that has been upgraded to FTTC. Their pricelist shows that you will be charged the distance-based installation charge based on the "radial distance to the relevant aggregation node," while elsewhere it mentions that "96% of premises are within 2km of the nearest AN". However, it isn't clear whether they will charge you for the nearest AN or the one associated with your cabinet.
If you lay your own fibre to the community, then you need your own location to house the active electronics, and need to fund a different way to connect it back to the internet back at some co-location site, probably using some equipment you'd own/rent there. BT's standard access network (FTTC, FTTP or FTTPoD) isn't going to provide the backhaul for you, and a standard ISP isn't going to carry your data.