The SLR rifle was the UK and Commonwealth version of the Belgian FN FAL  rifle, the main modification of which was removal of the fully automatic fire option.

Originally trailed with the FN knife bayonet the X2E1, amongst many other, the bayonet chosen for the rifle was a new knife bayonet with the bayonet blade similar to that of the No 5, 6, 7, 8, and 9 bayonets used on the No4, Sterling and Sten guns. Other versions of trials blades used a double sided blade similar to the Belgian FN49, and the X2E1 without the flash hider prongs (X3E1). The No5 was used as the basis of the L1Ax series of blades. The trials version of this blade was the X4E1, this is similar to the production versions but without any markings

The information in the tables regarding the various designations are those commonly accepted from the texts, however the official documents say that the differences are down to two things

L1A1 and L1A2 are the same with the protruding catch and the difference is in the blade grind, the A1 being a single grind the A2 being a double grind

L1A3 and L1A4, the earlier two with a sunken catch

I have problems with this information as it appears the differences were to allow for differences in manufacturers abilities, the L1A2 is only made in Australia and there are other subtle differences and the L1A4 was only produced late on in the bayonets life, so did the manufacturer re tool for a different grinding technique???? I shall have to look at my examples and do some digging. Any information is more than welcome.

Here is the official documentation taken from EMER, SA&MG V150, issue 1, May 1971. Page 3, paragraph 13.
L1A1 and L1A2. Introduced at the same time, these models have a crosspiece held firmly by two rivets against a shoulder on the haft. The pommell is also rivetted in position. The difference between the two models, in addition to amall dimensional differences is in the method of grinding the cuting edge. On the L1A1, the cutting edge is achieved by grinding equal angled flats on each side of the blade.

On the L1A2, the thickness is reduced in two stages. The larger flats having an included angle of 40 degrees and the flats ground to the edge having an included angle of 55 to 60 degrees. Amendment 1: This arrangement is to allow the manufacture of the bayonet by outside cutlers having regard to the best and most efficient use of their existing machinery.

The bayonet catch on both models protrudes from the pommell approx 1/4". The protruding catch was liable to be operated acidentally, causing disengagement of the bayonet

L1A3 and L1A4 To overcome the defect in the L1A1 and L1A2 bayonet, shorted catches were designed and the bayonets modified to accept the new catches. After modification, the bayonets were redesignated L1A3 and L1A4 respectively. Further defects concerning loosness of the cross pieces and pommels were corrected by introducing brazing as an ADDITIONAL or ALTERNATIVE to rivetting. To further ease manufacture, slight dimensional changes are permitted and although the marks are not advanced, a differences will be apparent. The grooves on some blades are shorter in length and with the grips removed, some shafts will be seen to be a different shape.

Amendment 2 dated (unclear on paperwork). GRIPS, bayonet, pairs are marked with the identifying data relating to either the Bayonet L1A3 or L1A4 and are fully interchangeable. As such, these are not indicative of a sub mark of bayonet. The bayonet will be referred to in (should read 'as'!) its generic description of BAYONET, Rifle, L1A1

Many thanks to Peter Laidler MoD(Army)REME 

Versions of the blade were made by the UK, Indian, Australia and Canada

My thanks to David Adams who supplied many of the photographs below

X1E1

Trials FN bayonet  uses a thin blade similar in style to the Belgian FN49

X2E1

Trials FN bayonet, also found in a shorter blade version

X3E1

Trials FN bayonet  similar to the X2 but without the flash guard prongs

LIA1

Issued with the sheet steel scabbard of the No5 and having a brazed crossguard. Grips are marked L1A1

Later versions have a shortened screw in the pommel and it loses a hole in the pommel, post 1958

L1A2

Authorized at the same time as the L1 the main difference is that he cross guard is riveted not brazed. Mainly made in Australia (without any markings on the grips and ricasso) and Canada as the C1

Australian produced L1A2, quality of these bayonets is higher than on the UK produced items.

Seen here with the pouch mounts for the scabbard.

Sectionalised L1A2 for demonstration purposes

Courtesy Kevin Adams

L1A3

A change to a recessed lock stud necessitated a change in the pommel casting. Apparently the changes were made as there were comments on the ease of removing the bayonet with the protruding catch during use in riots and encounters with civilians (Northern Ireland?). L1A1's were modified by milling out the recess in the pommel to the new specification

A version was trialed with wooden grips (

Converted L1A1 to A3 spec the waisted cross guard is evidence of this conversion as the L1A3 had a straight sided cross guard

Dress blade form converted L1A1

New made L1A3 with straight cross guard

B61 manufactured

Courtesy Kevin Adams

D62

Courtesy Kevin Adams

D67

Courtesy Kevin Adams

L1A4

Essentially the L1A3 with a riveted rather than brazed pommel, not produced till after 1970

Courtesy Kevin Adams

C1

Canadian made version of the L1A2

1957 produced parade version

Courtesy Kevin Adams

1959 produced

Courtesy Kevin Adams

1960

INDIA

Indian Version is like the L1A3 and 4 but with wooden grips, a similar version was trialled in the UK

With wrap around wooden grips this long bladed model has a L1A4 style pommel

1966 dated example

Courtesy Kevin Adams

MISC

Box of chromed tips for the bowie blade tipped blades, box contains 12 but has no marks on it

Fitted to a blade tip IT would effectively blunt the blade

Plastic scabbard for the L1Ax bayonets with a steel throat. This one came with a parade frog

An unfinished trials scabbard with distinctive square frog stud.

Production version of the trials scabbard, the trials versions are without markings. Apparently about 40,000 of these were made but few turn up, it is thought that most were destroyed in a warehouse fire and these are actually more rare than the actual trials ones themselves.

Note the distinctive "square" frog stud of this version