Hi Dave,
Looks like you have made a nice job of that boiler... well done.
Since you are in the UK the test requirements are: -
Hydraulic test to 2 x max working pressure... held for 20 minutes with no loss of pressure and with no external fitting attached other than the test pressure gauge (which must be a calibrated and certified gauge).
All fittings should then be attached except for the safety valve and the boiler hydraulically tested to 1.5 times working pressure... again no leaks shall be accepted and the pressure held for 20 minutes.
The safety valve should be set and calibrated against the test gauge and locked.
A steam test shall then be performed with all external fittings attached (and with the calibrated safety valve installed) with maximum burner and the safety valve should release at, or just below, the set pressure and check shall be made to ensure the pressure does not rise more than 10% above max working pressure (or the release pressure of the safety valve if this was deliberately set at a lower pressure) the water gauge shall be checked to see that it gives clear indication of the water level.
This water gauge can have a blow down fitted and if so then it should be operated whilst under full steam pressure and the water level should return immediately to the correct level when the blow down is closed again.
If a blow down is not fitted then the boiler shall be tipped so that the water level drops below the lower glass level and then checked to see if it returns immediately the boiler is leveled again.
The boilers small pressure gauge should be marked with a red line at the working pressure (as verified by the test pressure gauge) by the test inspector/engineer carrying out the test.
When all these test have been successful then you boiler can be certificated.
The hydraulic tests are valid for 4 years and subsequent repeat tests will only require to be done at 1.5 times working pressure. (unless any repair work has to be done to the boiler barrel assembly... in which case the whole 2x and 1.5x tests will need to be repeated.
The steam test is valid for 12 months and must be repeated annually.
I hope this clears things up for you... I assume you are able to get to a suitable model engineering club where they should have a boiler test engineer.
Good luck.
Sandy.