Those of you who have shared my pain over the years may recall my previous Sport Relief Mile, writes Lynne Mortimer.

My Sport Relief socks say 2012 so that’s when it was.

On that occasion, my friend Jane and I were overtaken by a toddler. This time, I challenge the under-4s to try and get past me (on foot) with my titanium knee.

“We can rebuild her. We have the technology. We can make her better than she was. Better, stronger, faster.”

Those are the opening words to the Six Million Dollar Man TV series which I have adjusted to suit. (Are you sure they’re adjusted enough, Lynne? ED)

OK, I take the point. I have been rebuilt, they had the technology. I am better than I was and more magnetic but not much stronger or faster.

I know this because I took George and baby Wil to an indoor play area, near their Essex home, last week. Wil, being one year old, was confined to a section entirely made of plastic-covered foam rubber. He knew he wanted more and promptly climbed out and headed for the bigger kids’ area. Six times I scooped him up before he got there. On the seventh, I changed tactics.

I tried: “No.”

He stopped. Looked at me and smiled as if to say: “You don’t really mean that, do you?”

So I put on my seriously grandma face and repeated: “No.”

Uncertain, he sat and looked at me, pointed at the 15ft slide he was interested in and smiled again.

“You’re too little, Wil,” I explained. Now I had offended him so he gave up trying to mutely reason with me and crawled towards the big slide. I dipped under the barrier, scooped him up and plonked him back in the baby area just as George called: “I hit my head, grandma. You need to kiss it better.”

I did. Just in time to stop Wil disappearing into the older children’s section. Again.

As a grandmother, I have discovered a whole new level of tiredness: exhaustion, weariness, prostration... a Thesaurus just doesn’t cover it. The nearest to it, I think, was when I was a schoolgirl doing logarithms in a double maths lesson immediately after lunch in the middle of winter with the classroom radiators blazing.

But I am confident I shall be able to complete my mile in under 40 minutes (my existing record). There is, however, one thing that might slow my progress. I am going to the hospital for a patch test. This is to determine what may have caused my face to swell up like a balloon, last April, before my skin peeled off. It’s been a bit of a wait for the appointment during which time my face has returned to normal... ie it’s as good as it’s going to get.

So on Monday, around 40 patches will be applied to my back and indelibly labelled. I am not allowed to shower so I shall probably be a bit whiffy. On Wednesday, the patches will be removed but the labels will remain and I still won’t be allowed to shower. Whiffy plus.

On Friday there will be a full review of my back to see what, if anything, has caused a reaction.

I have been warned that there may be something I didn’t even know about that makes me flare up. If this is the case, then I am going to have a very embarrassing weekend. On Saturday evening we are going to the Lighthouse restaurant in Aldeburgh to celebrate a friend’s mm-mth (65th) birthday. If my back is unbearably itchy I may have to use my fork and plunge it down my jumper... or order something with scratch potential. I’ve checked the menu and they don’t serve baguettes whole. A couple of oyster shells inside my vest might work although I have a shellfish allergy. The toffee crunch ice cream is a possibility.

Then, at 10am the following day, I shall be setting off on my mile for Itch... I mean Sport Relief. I have put some money in so I don’t have to seek sponsorship. It doesn’t seem right to ask people to shell out for me to dawdle a 1,760 yard Sunday morning stroll.

I am a little concerned about an itchy back. I am imagining having to stop at every lamppost. No, not for a Paula Radcliffe, for a scratch.

Meanwhile, my friend Jane, with whom I am walking, will probably disown me if I start rubbing myself up and down against street furniture.