Hi Dave
What part of Toxteth Park are you interested in? Alan Godfrey Maps have just published the St James' Mount large scale plan from the mid 19th Century, so most of TP above Upper Parliament Street (but only about 15% of the total) is now covered. There are also a few bits below Upper Parliament Street. Most of Toxteth Park would have been undeveloped in 1840-50.
If you google 'old ordnance survey maps' you should find links to a few resellers of OS plans of the period. These can cost £30-40 for good quality copies. Godfrey's use plans from the Scottish Library and the British Library should have copies.
If you are looking for a big-ish street then six inches to one mile will do. But if you are looking for say a court you will need the 50 inch (1:1250) series.
Ken
