Re:
Hi Mike
It's a great frame, the RL853. I would guess that's about a 2004, but it might be possible to tell for sure from the serial number (although unfortunately not all the builders they used over the years used a serial number format that reveals the date).
If it is around 2004, that P2 is ludicrously short for it, so it's a good job you're such a skilful rider! Even the SID would be a bit too short, although admittedly the long stem to some extent counteracts the effect of the short fork.
If the photo of the open gate is where I think it is, you deserve respect for getting up that hill. I'd definitely need a warm rhubarb scone with cream and rhubarb jam from Steyning Tea Rooms before even attempting that one!