Bank of England Ten Shilling notes issued from October 1961 had a serial number format of LNN (letter, number, number) followed by 6 digits, eg. A01 123456.
Serial numbers for this period commenced with the following letters -
A, B, C, D, E, H, J and K.
Replacement notes commenced with M and used the range M01 to M18.
These serial ranges may have extended into 1962.
I have no way of knowing whether or not it was circulated, but the serial number of the last Bank of England Ten Shilling note commenced with D38N and possibly ended with 999999.
Without additional context, the value of a Bank of England Ten shilling note with serial number 18Y 015906 would depend on factors such as its condition, rarity, and demand among collectors. I recommend consulting with a currency appraiser or a numismatic expert for a precise valuation.
Please check the serial number and provide the name of the Chief Cashier if possible.
It is worth 5 pence if you mean the English shilling
You have omitted the first 3 or 4 characters of the serial number and not provided the name of the Chief Cashier. Modern Bank of England One Pound notes were issued from 1928 to 1984. Please narrow down the possibilities a lot.
Custer
A Bank of England Ten Shilling note (Series A - red/brown)(Chief Cashier L.K. O'Brien - serial number B15Y), uncirculated and in absolute mint condition could fetch anything up to £40 GBP. If it has been circulated but still in good condition, it might fetch anything from £10 to £18 GBP. A reputable coin dealer will be able to give a more accurate valuation.
The lowest denomination paper note regularly issued by the Bank of England was the Ten Shilling note. During the 1930's, there was an attempt at replacing the Shilling, Florin, Halfcrown and Crown coins with paper notes. The Shilling and Two Shilling notes were not taken beyond the Proof stages. The Two Shillings and Sixpence and Five Shilling notes were produced in large quantities and distributed to banks, but were all recalled and pulped (supposedly). It seems that some were not returned. These notes could fetch a few thousand Pounds if the are in excellent condition. During the earlier days of the Bank of England, many banknotes of strange and non-standard values were produced, often hand-written. It is currently thought that none of those banknotes are known to exist.
A Bank of England Ten Shilling note (Series C - red/brown)(Chief Cashier J.Q. Hollom - serial 26H), uncirculated and in absolute mint condition could fetch anything £8 GBP. If it has been circulated but still in good condition, it might fetch anything up to £4 GBP. A reputable coin dealer will be able to give a more accurate valuation.
A Bank of England Ten Shilling note (Series C - red/brown)(Chief Cashier L.K. O'Brien - serial H90), uncirculated and in absolute mint condition could fetch anything £10 GBP. If it has been circulated but still in good condition, it might fetch anything from £2 to £8 GBP. A reputable coin dealer will be able to give a more accurate valuation.
A Bank of England Ten Shilling note (Series C - red/brown)(Chief Cashier L.K. O'Brien - serial A12), uncirculated and in absolute mint condition could fetch anything £12 GBP. If it has been circulated but still in good condition, it might fetch anything from £3 to £9 GBP. A reputable coin dealer will be able to give a more accurate valuation.
If your Ten Shilling note has Queen Elizabeth II on the obverse and a large image of a seated left facing Britannia on the reverse, a serial number commencing with S74 would be Chief Cashier J.Q. Hollom, possibly printed in 1963.