Found the PCP and know where cabinet is know however it seems far away from PCP c.300m, would this affect speed
The fibre twin cannot be 300m from the PCP.
That absolutely would affect speed, massively.
The fibre cabinet is usually within 50m, but is built as close to the PCP as possible.
AIUI the maximum distance is around 100m, though I've never seen 1 that far away.
It would be a monumental screw up if a fibre cabinet has been built 300m from its PCP.