The True History and religion of India: A Concise Encyclopedia of Authentic Hinduism, written by Swami Prakashanand Saraswati, is an interesting book You can find information on it in the following address, in case you are interested in procuring a copy.
http://www.thetruehistoryandthereligionofindia.org/
The book gives insight into the history of Hinduism and its practices, from a perspective that differs from those found in many other works, mostly written by western Indologists (Max Mueller, William Jones, etc.). In the book, Swami Prakashananda addresses the interpolations that were deliberately introduced in the vedic texts on number of issues, by various rulers in different time periods before the British, and then by the British.
On the issue of vegetarianism, he states that interpolations were introduced that suggested that meat eating was acceptable, and recommended from a religious point of view, primarily to accommodate the various ruler’s personal food preferences and habits. There are several pages and sections in the book devoted to the issue, with references to verses from the various texts such as Manu Smriti, Poorv Mimansa, etc., . I have quoted verbatim some passages from the book, enough to give an idea (I have tried to ensure that the quotes are verbatim, but may have inadvertently missed out a word here and there).
On the interpolations in the scriptures in general, he says: (pg. 334)
There are three kinds of fabrications: (a) altering only few words of verse to change its meaning, (b) creating new verse of the desired meaning, (c) creating full new section of a chapter to elaborate the killing and meat eating episodes.
On why and how these interpolations on meat eating came about: (pg. 330-336)
…We have to look into the history before the advent of Guatama Buddh when there were chatriya kings who ruled various parts of India. Those non-vegetarian worldly and ambitious kings, presuming to receive heavenly luxuries, had started to do animal sacrifices in the name of yagya. It’s the nature of kaliyug that once a wrong and unholy transition starts in the world, it grows like bush fire. The same thing happened with this tradition and all the kings and the landlords, big or small, excessively started doing animal sacrifices and the poor brahmans, in the greed of getting money, supervised and conducted such yagyas.
There is a greater probability that during that time, the powerful kings, to religiously justify their wrong deeds of killing and eating the animals, made the brahman scholars create such verses and chapters that should exactly match the literary style of the scriptures and added them in the Smritis, Grihya sutras and Dharm Sutras, etc., as they were the main religious books related to the ritual performances. Statements of meat eating in shradh and offering it to god and offering meat to guests as compulsory act was also added in the Smritis etc., wherever there was chapter on shradh. During that period Gautama Buddh came and taught the lesson of compassion on all the beings…
….There was a big change in the history of India when the Han and Shak tribes began to invade and started settling in North India...There is a greater possibility that during that period also lot of similar interpolations concerning the animal killing and meat eating would have been done in the Smritis and the Sutras and subsequently the interpolations of offering meat in shradh to brahmanas and the gods would have also been added in the Puranas…
…impious interpolations in Smritis and Sutras, etc were not the work of one single period, they must have been done during the span of thousands of years and under the instructions of the ruling kings of that time, because the wordings themselves give a smell of perverted sovereignty…
Swami Prakashananda cites verses from the various texts, to demonstrate the inconsistencies in their recommendations, and suggests that these inconsistencies are as result of delibrate tampering with the original texts.
In the later sections, he details the role of the British indologists in promoting the interpolated verses to their great advantage, in order to destroy Hindu religion and culture.
…They knew that Hindus adore their sages, saints and acharyas. They are vegetarian and have great regard for the cow. Thus, with one blow, they tried to crumble the faith of the Hindus in their Vedic Sages. They vigorously promoted such ideas which showed that Vedic brahmans not only ate meat but they loved to eat meat as a must. In this way they imposed their personal characteristics upon Hindu Sages.
The Greek gods and goddesses were pleased with animal sacrifices, Roman gods were of the same kind, God of the Bible loved to demand frequent animal sacrifices from each and every house. Thus, because such things were in their own religion, the English people tried to abuse the Vedic yagyas and the Vedic religion in a similar way... (pg. 338)