I just received these from an ebay seller. I don't believe two cancels have been previously seen- Colebrook and Clarememont, ( ref John Hardinge, Courier Edition 52, p8) . These two are straight line railway issue type R4 rubber. The Devonport has certainly been seen before. I think its "Devonport Cancelled", date on 1 line in the centre.
If anyone has seen these before I'd be most interested to hear. There are many other not yet seen railway cancels - see the above reference . The article appeared in the most recent edition of The Courier and is a fascinating account of a little-know aspect of railway/telegraph/postal history.
Any other examples of these cancels would also be most appreciated.