RAPA,
The point that the previous posters were making is that in Germany you and the 737 are in the same Wake Turbulence category. ie You are a Medium under ICAO rules (>7tonnes). In Germany therefore, there is no requirement to give you the 2 minutes you were expecting. The CAP 493 is for UK use only. When the Tower controller replied that you had 4 miles they were probably trying to re-assure you that the preceding aircraft was clear ahead, they would not be thinking that there was a Wake Turbulence issue. Under ICAO rules you are a Medium category aircraft and that is what will appear on your flight plan info. This info will be used on both departure and final approach phases of flight. Do I think (as a UK ATCO) that it's a good idea to launch you up the chuff of a 737? Not really, but ICAO says its okay. Next time, whilst you are at the holding point, advise the controller that you are requesting a 2 minute gap before you are airborne.
Regards, ADIS