Dear OP,
There are always ways to gain experience and get a job in a field you are interested in. A 3rd should not stop you, not everyone is made for academic study. I have a friend who graduated with a 3rd and now works as an engineer earning 50k simply from practical skills, experience and the right attitude. the first role as a trainee engineer working in robotics came through networking. There is a certain amount of 'who you know' and luck, but there are some things you can do to help it along.
a few suggestions
- contact your university careers service for an advice session and potential employer contacts - many universities will offer support for a number of years after you graduate and often run excellent careers events where you can speak to several employers. If you have someone there who is responsible for internships/placements or employer engagement, get in touch with them. the careers information team (those that answer the phone when you ring) will know who to put you in touch with to speak to them.
- contact the Open University (or yours) and ask to speak to a disability adviser - they will be able to offer some help in disclosing your previous or current medical issues to an employer and this will help you talk about your degree result in a more positive way, if this is something you are worried about.
- some of the larger companies e.g. EY (not engineering I know) are dropping their degree requirement for graduate recruitment, I would perhaps not focus too much on the larger graduate schemes and look instead for 'graduate jobs' as these are not the same thing at all. A graduate level job is a role you would usually go into at an entry level, a graduate scheme is a training programme with a job at the end. the second is much more competitive and it is well known that there aren't enough Graduate SCHEMES, for the number of new graduates every year.
Think about what your strengths are, what you are good at and how you got through your degree - what motivated you and what skills did you need/develop?
did you do anything to enhance your knowledge/for your own enjoyment of engineering whilst you were studying? this could be brought up when speaking to an employer also.
Which engineering professional body accredited your degree? They will have a list of skills that you will have achieved as part of your degree regardless of result and this is one way you can sell yourself
Make professional friends on linked in - choose a few small companies that you find interesting working in a field you like and just say hi. once you have exchanged a few pleasantries (be sure to complement the company and make reference to something interesting they are doing) you can ask if they have any advice for you in relation to gaining experience. You need to bypass the recruiters and speak to someone technical who will understand your situation.
finally, go to job fairs, not the london grad fair etc, but ones that focus on areas of interest or up and coming areas - future tech in cities for example. get on the mailing lists of the catapults and start talking to some of the SME's that are under the business incubators there
although it is not ideal, there is always volunteering as well and these smaller companies will definitely appreciate the additional help. you can offer a few hours only if you are already working somewhere else.
I hope this helps, you just need to do some research, make some contacts and I'm sure you can past that first barrier
Good Luck!