Only for IMC holders when IFR in Class D or G airspace. For IR holders IFR in class A airspace minima is procedure minima/company minima/absolute minima but only if there is a published procedure. For IR or IMC holders SVFR in Class A and D minima is 3km, see Schedule 8 and any 'notifications'.
3km is required in London CTR within Fairoaks, Denham and White Waltham Local Flying Areas. See ENR 1-4-2 2.1.1.1 para (vii)(a). It is a 'notification', ie. a 'special concession' within the London CTR Class A airspace and should not be abused, as it often is.

So what about exemptions for high performance aircraft and paras?

Are these treated as SVFR or VFR or IFR, with out full compliance?

To further muddy the waters, back to the weather minima; according to the ANO schedule 8, sub-section 2 (priviledges of a PPL (aeroplanes):-

A pilot shall not ......

para (c)

unless his licence includes an instrument rating (aeroplane) or an instrument meteorological rating (aeroplanes), fly as pilot in command of such an aeroplane:

(ii) on a special VFR flight in a control zone in a flight visibility of less than 10 km except on a route or in an aerodrome traffic zone notified for the purpose of this sub-paragraph.

This also applies to a holder of a BCPL (aeroplanes).

So a basic PPl holder (no IMC rating,etc) can fly VFR in a class D CTZ with 5km visibility, but is unable to accept a special VFR clearance!:hmm:

True, but a SVFR clearance exempts you from the 1000ft rule (formerly 1500ft) under rule 5, so I guess better viz. might be a good idea (not that it will help you when the engine quits).

Tim

Actually - not true. Read the proviso

Why do you think Class 'D' airports have entry / exit lanes notified? So bare PPL's, when the vis is between 3 & 5km (day) or 3km & 10km (night), can arrive or depart at an airport in a Class 'D' zone provided they route via the lane and fulfill any criteria required for its use.

Also means they can fly circuits SVFR in the above met conditions.

Sorry Chilli, but I beg to disagree.

Checking the AIP page ENR 1-4-5, there are 28 class D ctz's, (CTA's not counted, as SVFR does not apply).

11 are notified for the purposes of schedule 8, but 17 are not.

So my comment is true in the majority of class D ctz's.

Only for IMC holders when IFR in Class D or G airspace

OK, I should have quoted a bigger piece.

I think IMCR holders are stuck with the 1800m min met vis on any IFR departure or arrival, no matter what the airspace class is.

Do you have a reference for lower permitted forward vis when operating at a Class E or F airfield? That would be serious news to me. Doesn't affect me (have an IR) but interesting nonetheless. I know there is very little E or F in the UK...