Lifeistooshort your most welcome.
Ok few more bits of information for you.
You'll probably find your progression in aikido is slower to start with them with karate. On the flip side as you have a good grounding in one ma and the mindset you'll find that side of things easier probably.
If your interested in the weapons side of aikido (jo, tanto and bokken) you are going to need to find a good school. I would look for a dojo that is a member of
JAC (Joint Aikikai Council of Great Britain) - JAC is the official governing organisation for traditional Aikido in Great Britain. It is recognised by Aikido World headquarters. That way you are garanteed that your dojo is Affiliated - Look for affiliation to World Aikido Headquarters in the case of traditional aikido. Be aware that only a few dojos in London, and indeed the UK, have this affiliation. Your Aikikai grades will be recognised and your training consistent all around the world. This will not be the case with privately issued grades. Ultimately this is a question of quality too
Ok brief word of warning there are some centres in the UK (actually everywherr outside japan) that have instructors and offer students private grading systems this means that there are SOME people with very high grades that are not trained to the right standard. I want to be careful here I am not criticising these centres but they are not necessarily as good as their dans would indicate. (Eg they may hold a privately graded dan above mine but my training and competency will be above theirs) By studing with a JAC school you will be getting the same level of tutition as you would in Japan. Hope you see what I mean.
Some dojo will offer classes which are devoted almost exclusively to training with Jo (staff), Tanto (knife), and Bokken (sword); the three principal weapons used in Aikido. However, the goal of Aikido is not primarily to learn how to use weapons, so I would always recommend a 1 in 3 ratio for every weapons class you should do 2 none weapons classes. This is the same percentage of weapon vs none weapon training persists throughout aikido
Ok so things you can and probably should ask
So you've found a JAC centre
Ok go and talk to the instructors what grades are they, who awarded them (they should have no problem with you asking this) have they done national or internal study?
How often do the offer classes (i recommend 2 classes a week to New students)
Can you observe a class (I'd have no problem with this but I do ask that you show respect to my class and students so please be quiet - I'm sure you would be anyway)
Are the students and instructors respectful?
Remember aikido training is cooperative not competitive I can explain this in more detail but just wanted to give you the basics as I don't want to over load you.
As your looking for weapons training when do they offer this? A student can train with weapons from day one but should train with weapons after they have a basic grounding some schools don't offer weapons training at all. So you will possibly be told either at a certain belt or once you reach x standard or they may offer weapons classes as an additional class option.
Hth?? If there is anything else please come back to me, honestly more than happy to help.
If your looking for more weapons focus than aikido offers there are other more weapon focused ma which you maybe interested in I can discuss a few of the japanses options if it would help.