Great Britian (not offshore)

7 Parameter Helmert Transformation,
 |X|   |X|    |Tx|   |  0  -Rz   Ry |   |X|       |X|
 |Y| = |Y| +  |Ty| + | Rz   0   -Rx | * |Y| + D * |Y|
 |Z|   |Z|    |Tz|   |-Ry   Rx    0 |   |Z|       |Z|
    T     S                                S         S

T          ... Target Datum 
S          ... Source Datum 
Tx, Ty, Tz ... geocentric X/Y/Z translations  [m]
Rx Ry, Rz  ... rotations around X/Y/Z axis    [radian]
D          ... correction of scale            [ppm]

see
Boucher, C., Altamimi, Z. (1992): The EUREF Terrestrial 
Reference System and its First Realizations. 
Veröffentlichungen der Bayerischen Kommission für die 
Internationale Erdmessung, Heft 52, München 1992, pages 
205-213 (1) 

REMARKS: in (1) correction of scale D is included in the 
rotation matrix 

******************* Attention *******************
In some transformation applications a different formula 
than the formula above could be in use. The signs and order 
of the rotation parameters are then define differently and 
rotation unit can be arcseconds. For test purposes you can 
find in this information system verification data to check 
your application to get correct results. 
 
Distinguish the following cases:
a) change of signs of rotation (Coordinate Frame Rotation)
   Rx = -Rx
   Ry = -Ry
   Rz = -Rz

b) change of signs and order of rotation 
   Rx = -Rz
   Ry = -Ry
   Rz = -Rx
******************* Attention *******************

OSGB36 is an inhomogeneous system by modern standard, 
generally accuracy 2 m, in some areas it is no better than 
5 m, see www.gps.gov.uk for a more accurate transformation 
in 1 km grid areas (registration for internal auditing 
purposes neccessary)