Hi Lancer!
I can give you approx. distances and road conditions 'cause I just had travelled (May'09) KHI-ISB-MURREE-LHR-KHI.
KHI-SKR: 450 KM (6-8 hrs), SKR-SHWL: 680KM(8-10 hrs) (???) and LHR is about 170KM (??) (3-4 hrs) from Sahiwal.
NORTH BOUND:
Road Conditions KHI-HYD: you will have diversions past nooriabad till HYD Toll plaza and then past Sakrand you have intermittent diversion till Pano aqil and after that its all generally smooth sailing till LHR except a bit or two bump around UBAURO.
SOUTH BOUND: Its all smooth sailing till you enter Sindh and then its mostly bad road conditions and diversions till Qazi Ahmed and then diversion past HYD Toll Plaza.
CNG: abound all the way to LHR no problem at all but only use TOTAL, ADMORE etc and avoid private CNG stations as much as you can because of their haphazard maintenance regime. Branded are expensive but safer since a friend of mine end up having air-mixed CNG with lot of water contents in his car at somewhere around MORO.
Assuming you have 55 KG cylinder with good mileage you should have filling stops at 1) KHI PSO P/P 3 KMs past Al-ASIF Sq. can't miss it with big ROUND PSO Sign and right after total pump with lot of dumpers filling up.
2) HALA TOTAL on your right north bound
3) ADMORE Ranipur or Gambat then you can top-up at SKR
4) ADMORE SADIQABAD/RYK Chowk Bahadur
5) TARANDA
6) BWLPR by-pass Lodhran then
7) Kacha Khuh-Mian Chunnu and then Sahiwal
RECOMMENDATIONS:
1) Since you are on a LHD car, which I will not recommend on the H'WAY but since you have decided than you have to be extra careful on diversions and single road due to two way traffic on single roads and I will recommend you to switch to PETROL on these roads for better overtaking.
2) If you wish to take Lodhran by-pass to Khanewal which ends up at Niazi Chowk, Khanewal and its just past the railway crossing at Lodhran but road is just OK and SINGLE and you have to deal with heavy traffic although its true the roads around Multan are underconstruction and about 70% laid up and ready for carpeting but they are SAFE esp. with you having LHD car.
3) Leave early morning say 4-5 o-clock, you will be able to avoid bi and motor cycles, ChinqGIs, and tractor trolleys till 7 in the morning and your out turn will be lot improved. avoid travelling in the night as the dazzle from the buses and trucks will slow you down as well as a bump from an expected pothole or a speed cum back breaker.
LHD! a BIGGER RISK then you THINK
Hope you are a satisfied person now and HAVE HAPPY JOURNEYS,
CHEERS,
Kaleem