+25 lbs boost on 100/150 grade was cleared for the Merlin 66 in March 1944 (http://www.spitfireperformance.com/25lbs_approval.jpg) and entered service with the Preddenack Wing's No.'s 1 and 165 Squadrons in May (http://www.spitfireperformance.com/no1_25lbs.jpg). They continued to use it through at least September. The Griffon 65 was tested at +25 lbs boost but was cleared for +21 lbs boost. By the end of February 1945, 2nd TAF's Spitfire IX and XVI wings were all using +25 lbs boost and the mk XIV squadrons at +21 lbs.
ADGB's Mustang III/IV squadrons converted in late February/early March 1945, although No.'s 129, 306, 315 and 316 utilized +25 lbs boost from early July until at least mid-September.
As for the enigmatic 'Basta' modification, I have seen it mentioned with reference to MTO Spitfires but there is absolutely is no evidence that 100/150 grade fuel made it the MTO for either the RAF or USAAF. If the ASR Spitfires were LF IX/XVIs, then it is possible, though unlikely, that they received +25 lbs boost.
All the details (including Mosquito use of +25 lbs boost) are covered here:
http://www.wwiiaircraftperformance.org/150grade/150-grade-fuel.html
Also, note that USAAF VIIIth Fighter Command converted entirely to 100/150 grade in late June 1944, although the V-1650s in USAAF service were limited to +21 to +22 lbs (72" to 75" Hg) boost.
HTH,
Brent