NOTES ON NEW CATS
FROM CELIA HADDON, DAILY TELEGRAPH

SHOULD YOU DO IT ANYWAY?
Your responsibility should be primarily for the cat or cats already in your care. Think hard before asking an very elderly cat to put up with a new companion. Kittens will be accepted better than an adult cat, but kittens often pounce on and pester old cats. Some old cats will mother a kitten; others (like my eight year old) definitely won't! It can take months and months for harmony and sometimes the cats will never be friends. Cats which are used to a multi-cat household will be less upset than a cat which has lived alone. Get a kitten from a cat shelter, which will promise to take it back if the introduction really doesn't work out. A male female mix is probably better than all female.
Be careful about accepting the local stray into your home. Ask yourself if an existing cat should have to put up with a former stray, who may bully her/him. In the case of a stray cat, you can feed it, then when it is tame enough find it a new home via the Cats Protection League or the Blue Cross.

THE INTRODUCTION
The best way to introduce a new cat is to give it an indoor pen with food, litter etc. If you can't borrow or buy one, give the new cat its own room, so that it feels it has safe territory. Shut doors windows, and block chimneys before letting it out. If possible a retreat hole like a covered cardboard box with entrance hole, or a cage-den . Put familiar toys (if available), feeding bowls etc. in the room. Put litter tray in the room. You can't expect a cat to go outside in the first few days, and if you let it, you may not see it again.
Mix the smells. From the point of view of a cat, anything which smells strange is an intruder. Give the new cat something to sleep on which smells of the old cat, then visa versa. Using same grooming tools on both cats. Pet one, then go to next room and pet the other. Transfer used litter from the new cat tray to the old cat's tray and visa versa to mix smells.
If you have a large indoor pen, all this can be done while the kitten spends time in the pen. You can start feeding them in the same room one in the pen, one out of it and the other side of the room. Each day bring the bowl of the one outside the pen nearer the pen.
Vets can sell something called Felifriend, a spray or wipes. Felifriend sends a pheromonal signal to a cat that another animal (or person) is familiar and non threatening. Some behaviourists have also used it with success when introducing strange cats to each other or trying to resolve inter-cat conflicts. Felifriend is available through vets although not all of them will have it in stock (usually available within a day). The price will vary depending on the practice but I expect it would be in the order of £9-50 per bottle.
If your vet refuses to get you this, get Feliway. It's not quite so good for this kind of thing but it reduces anxiety and will therefore help. Spray it at chin height on things a cat would rub with its chin, all round the new pen and the room where the pen is.
If you don't have a pen, first transfer all the smells while the new cat is in the separate room. Then use a cat box with the new kitten in it for the first introduction. That way, they have the chance to see each other in safety. Watch the body language closely. Introduce the animals together when the new cat is used to his room and territory. Make sure there are escape routes for whichever cat wants to run away. Do not leave strange animals together alone. You must be there to make sure accidents don't happen.
Staring, puffing up fur, hissing, growing etc may happen. This is OK as long as it isn't translated into aggressive action. Do not intervene unless you think one cat is being seriously hurt. Do not pet the newcomer in front of the old cat to begin with. Give the old cat extra affection.
When the animals begin to accept each other, feed them in the same room. Supervise feeding and make sure there are escape routes for the cat which wants to run away. Slowly bring feeding bowls nearer (in the case of two cats not dogs) This will take up to four weeks. Be careful of letting the new animals out -- give them about 3 weeks inside first. Make sure that the first time, there is an easy way back inside the house -- ie. don't expect a new cat necessarily to know about catflaps, leave an open door.
Accept that they may never be friends. If they tolerate each other, that should be good enough. Try to make sure they both have safe places to retreat to. But if one cat is seriously bullied -- not able to eat without being hassled, ambushed on its way in and out of the litter tray, harassed in its cat bed, spending all its time under the bed, then think of rehoming.
There is a new product called Feliway, which may help if an insecure cat starts spraying. Get it and advice on how to use it, from your vet.

OTHER PROBLEMS
The CPL has a free leaflet called Living in Harmony, send a large s.a.e. and a few extra stamps to Cats Protection League, 17 Kings Rd, Horsham, West Sussex, RH13 5PN. They also have a leaflet called Moving House With Your Cat, which may be relevant. I have some notes on cat-hating dogs, but, on the whole, a cat should not have to live with a cat-hating dog -- the daily stress will be too much for the cat and, of course, it may eventually be killed outright.
Consult Introducing our cat to other cats and dogs on www.fabcats.org or send an s.a.e. and small donation for it to Feline Advisory Bureau, Taeselbury, High St, Tisbury, SP3 6LD.