Well there's "Good News & Bad News"
The good news is that the BPW96 photo transistor with a 10K Pot did the trick. Also the signal doesn't need inverting.
Now I send this request message @ 300 Baud 7bit Even Parity one stop Bit
2f 3f 21 0d 0a /?! {cr}{lf}
Then get this reply...
2f 41 4d 50 30 35 31 39 36 41 2d 36 31 42 0d 0a /AMP05196A-61B {cr}{lf}
(This is the model of the meter)
All well and good. 
Now for the bad news....
If I send an acknowledgement and read command I get no reply.
This should give me a meter read but unfortunately returns no data.
Just as a test I sent an Acknowledgement with the programming command
06 30 30 31 0d 0a .001
And got this supply
01 50 30 02 28 30 30 34 30 29 03 64 .P0.(0040).d
Which from the I.E.C. specification means give me a password using a manufacture specific algorithm and 0040 is the key.
So my conclusion is that "Yes you can make an optical port for less than a couple of £'s" but not all meters allow you to read them without a password.
A lot of meters give up there data only after the initial handshake. Others like the Elster A100C dribble the data out constantly without any request.
So now I need to go to plan B a current transformer. The optical output goes solid red when the power when the power flow is reversed so combined with a current transformer I should be able to get the data I need.