Ok an opening bit on British nightfighter ops:

These were typically flown at 15 to 25,000 feet. There were two basic types:
The support operation where the fighter flew in support of the bomber stream. These flights could be done on either side, behind or, above the bomber stream.
The intruder operation where the fighter flew independent operations away from the bomber stream(s), often orbiting near known German nightfighter airfields waiting on returning aircraft.

There were three basic 'modes' of operation which relied primarily on ESM measures to begin the interception. These were:

Serrate: Serrate was a ESM device designed to home on Lichtenstein B, BC and C emmissions. Later models were developed to home on the SN-2 model also. There were several different marks of Serrate and all operated roughly the same varying in details. Serrate displayed on two small CRT screens mounted side by side with the traces set at 90 degrees to each other (one horizontal, one vertical). A set of herringbone lines would emminate from the trace to each side of it when a detection was made. The longer these lines were the closer the target was. The side of the trace showing more lines (they were asymmetric in output) showed the relative position of the target...left / right, above / below. The operator could by this method talk the pilot into an intercept position where the AI radar could then pick up the target (maybe, hopefully....) and complete the interception.
In practice early models of Serrate proved susceptible to false indications from Würtzburg radars and in some cases, Freya as well. Directional indication was also found to be insuffficently fine to often turn contacts into interceptions. It also didn't help that most Serrate nightfighters (usually a Beaufighter) were equipped with AI Mk IV.
AI Mk IV radar was a metric (1.5m wavelength)set. Its performance was roughly equivalent to Lichtenstein SN-2. It suffered from poor minimun range (about 800 meters), and interference from Window and bomber stream ECM outputs that decreased its effectiveness considerably.
With later model Serrate devices with improved sensitivity and better AI radars in service it proved a valuable tool in making interceptions.

Next was Perfectos. Perfectos was, in theory, the perfect ESM homing device. It gave everything necessary for a successful interception....in theory....
What Perfectos did was interrogate German FuG 25 Estling IFF systems and get a response. The operator, like with Serrate, could then direct the pilot onto the target, which was definitely an enemy, by similar methods to those of Serrate.
In practice, Perfectos proved insensitive enough to often bring the using aircraft into contact range (bearing accuracy was about + or - 3 degrees). Also, the German pilots figured out that their IFF was being messed with and often left the sets turned off prefering to take their chances with their own flak to those of being shot down by a British nightfighter. Again there were several models differing in detail in use.
Perfectos was also used by the USAAF in daylight operations as an early warning system. Somewhere I have a photo of a P-51B equipped with it too which might make a neat model as the plane is sprouting whip antennas from everywhere!
Anyway, perfectos equipped squadrons were typically Mosquito equipped and had AI Mk X (US SCR 720) radar systems. This radar proved highly successful and resulted in a good number of intercepts on its own. It was largely uneffected by jamming and Window due to it being a centimetric set. This was probably the most successful airborne nightfighter radar of the war.

The last ESM set the British used was Monica. This was really a tail warning radar that had been in widespread use with Bomber Command....right up until a captured Ju 88 with Flensburg showed it was being used as a homing device to lead German nightfighters to their prey.
In nightfighter ops, the British turned this knowledge into a means of ambush. The nightfighter with Monica radiated allowing a German nightfighter to home on the plane. Once the German had closed to about 3000 to 5000 yards and Monica indicated a contact the British pilot was instructed to perform a "Whiting maneuver." This was a racetrack turn designed to bring the British nightfighter around behind its quarry and return it on its original course, now behind the German stalking it. As most Monica equipped nightfighters had AI Mk X (Mosquito) or AI Mk XV (US AN/APS-4) (Mosquito or Beaufighter with thimble nose) and both of these sets being very accurate centimetric radars it was usually possible to convert these contacts into an interception and often into a kill.

It is important to note that in all cases it was more the availability of good or excellent AI radar rather than the ESM system that allowed contacts to be turned into a kill. The ESM only allowed the nightfighter crew to initiate contact, something all three systems described were very good at doing. But, it was the use of the AI Mk X and XV that allowed contacts to be converted into successful interceptions.

Also of note is that British nightfighter operations had an effect on the morale and efficency of German crews far out of proportion to their successes. For most of 1944 the British only had a few dozen successful interceptions. The Germans lost far more crews through inexperiance (crashes etc) and to bomber defenses than to nightfighters. But, because of this out of proportion impact the British were highly successful in reducing German efficency.