Did the Gospel Standard Baptists and the (original) Plymouth Brethren comment on unity between themselves? It seems to me a great shame that the Gospel Standard Baptists, in the days of such as J C Philpot, during the mid 19th century, did not have some kind of unity with the early movement of the Plymouth Brethren, in the days of J N Darby. 

Both movements separated within their original bodies because of the controversy regarding the Eternal Sonship of the Lord Jesus Christ (I am quoting the title of J C Philpot's book on the subject).

The Plymouth Brethren split from what then became the Taylor Brethren (who said that Christ was only 'son' by virtue of incarnation) and the Gospel Standard Baptists were so-called because, after separation from other baptists for the same reason, they rallied to a publication, the Gospel Standard.

Both movements had their faults, but had they joined in unity, it seems to me, they would (one hopes) have been the means of correcting, or at least curbing, the faults of one another.

Is there any evidence, historically, that they had any thoughts of unity with one another ?
Introduction: The Gospel Standard is a Strict Baptist magazine first published in 1835 by William Gadsby.  Churches which align themselves with the magazine are known as "Gospel Standard Baptists" or "Gospel Standard Strict Baptists".  https://www.gospelstandard.org.uk/Magazines/Overview

Here is an extract from an article about the ‘English Strict Baptists’ which discusses the desire of The National Strict Baptist Federation (formed in 1946) to achieve unity.  The article concedes that the Federation has not brought the desired unity, even though efforts were renewed between 1962 and 1965 to obtain such unity.  The following conclusion is reached on page 35:


  If these Churches are to give the world a valid reason for their separate existence outside the Baptist Union, and to halt the decline of congregations and closure of chapels, something very drastic needs to happen. The prayer of those of all generations who are genuinely concerned about this sad state of affairs is that there will be a wholesome return to the doctrines which were held dear by the Particular Baptists who formulated the 1677 and 1689 Confessions of Faith.  It is believed that by a return to such doctrine there will come reform, renewal and unity amongst the Churches.  Source: https://www.biblicalstudies.org.uk/pdf/bq/21-1_030.pdf


So far, the drastic does not appear to have happened.  

A different source of information https://www.the-highway.com/Sonship_Preface.html  comes from a book written in 1860 by J. C. Philpot of the Baptist movement entitled 'The True, Proper and Eternal Sonship of the Lord Jesus Christ': 


  Today, some appear to be Exclusive Brethren and are headed by an Australian man, (and administered from Australia) calling themselves 'Plymouth Brethren' but their teaching contradicts the Leader of that, original, movement (J N Darby) who is quoted as saying: “If I hold the Son only as son from incarnation - I lose everything.”  


From what I have discovered, the Brethren movement split in 1890.  One section led by F. E. Raven (the cause of the split) was succeeded by James Taylor Senior, who held at least some of Raven's views.  Raven and Taylor taught that the expression 'son of God' refers only to the One who came in flesh after his incarnation and not before.  Those who disagreed with this view, holding to the ‘eternal son-ship of Jesus Christ’, departed.

Conclusion: I have not found any evidence to suggest that the Strict Baptists and the early Plymouth Brethren attempted to reconcile their differences in order to achieve unity.  Of course, that does not mean no attempt was made.  However, the sad fact is that both groups have gone their separate ways, resulting in isolationism.