Value will depend on condition and originality. The Mk V was only made 2 years, and about 2,000 produced. Rather scarce rifle, significant collector interest. Yours will need a hands on assessment by a dealer experienced in these rifles.
An SMLE rifle comes in three types: SMLE Mk III - 1132mm / 44.57" SMLE No. 4 Mk 1 - 1129mm / 44.45" SMLE No. 5 "Jungle Carbine" - 1003mm / 39.49"
Value of ANY gun is based on exact make, model, condition. If your Lithgow SMLE is original and correct, depending on condition it can be worth from $500-$1000.
A SPORTERISED SMLE .303 RIFLE WITH A THUMHOLE STOCK.
303 was the .303 inch diameter bullet that was fired by the Short Magazine Lee Enfield- or SMLE. Standard rifle of the British military from 1907 to the1960s, and still in limited use today.
A sporterised Lithgow .303 SMLE
Google the phrase and you will get hundreds of hits.
Assuming you mean a British MILITARY rifle, such as the SMLE, between $100-$350, depending on condition and originality. Rifles that have been "sporterized" lose much of their value as a collector's item.
The SMLE. Short Magazine Lee Enfield rifle. Picture above.
Moderately scarce. The SMLE 1 was produced 1904-1926, making yours a first year production rifle- but they did make a lot of them.
Bren gun, Lewis gun, SMLE rifle
S-short rifle M-magazine fed L-lee E-enfield
The Lee-Enfield rifle, (SMLE Mk III).