Is converting DVD to a format to play on a tablet legal (in the UK)
Please note this is UK legislation
After some research I found the following in a Government consultation paper:
From MODERNISING COPYRIGHT: A modern, robust and flexible framework
http://www.ipo.gov.uk/response-2011-copyright-final.pdf

There is a clear mismatch between what is permitted by law and the type of private copying that most people think is reasonable. The current law imposes unreasonable restrictions on consumers and may restrict the range of products and services available to them by limiting opportunities for technological innovation. In response to this, the Government will introduce a narrow technology-neutral private copying exception which applies equally to all types of private storage and all types of copyright works. It will allow a lawful owner or buyer of a copy of a work to reproduce that copy for their personal use, but would not permit them to share copies with other people.
This exception would therefore permit someone to copy music from a CD they have bought onto their mobile phone, or to back up an eBook onto their computer hard disk or other private storage, whether held locally or remotely. It would be allowed regardless of contract terms to the contrary. However, it would not allow someone to give copies they have made to friends, family or the wider public, nor would it permit copying of rented, borrowed or streamed content.

And

A permitted act that only allows copies to be made by and for a person who lawfully owns[41] an original copy will remove restrictions on the use of copyright materials that most people consider to be unreasonable and unnecessary, while drawing a clear line between acceptable personal copying and unacceptable sharing of copies. Consumers appear to recognise that sharing copies can harm creators and the Government does not want to dilute this message. Rights holders will therefore still be able to offer family copying and other licences that add value over pure private copying by individuals. They will also remain able to use technological protection measures (TPM) to restrict copying of works as and when they wish to do so.

[41] - This would include downloaded digital content that has been purchased to keep (or licensed in an analogous way) such as eBooks or film downloads, but not rented or streamed materials.
So, as I read it, you can make copies of CDs, eBooks, DVDs/BluRay if and only of they have no TPM on them.

CDs don't have TPM so copying (format shifting) is legal.
eBooks have TPM so copying is illegal.
DVDs/BluRay have TPM so copying is illegal.

But, it's the act of 'breaking' the TPM which is illegal. not the actual copying as long as the copy is for another device (format shifting) or for an archive/backup copy (whether on a local hard disc or a remote storage facility (the cloud)).
So, clear as mud really !